The 1959 version of Sam-Il was surprisingly different from the modern version.

In 1959 General Choi published his Taekwon-Do Teaching Manual. His earliest book, it contains instructions for five Ch'ang-Hon patterns plus 19 karate kata, including the three Taikyoku, five Heian, and three Tekki/Naihanchi kata.

No one has fully translated the 1959 book because it has a mix of Korean and Chinese characters. This was not unusual at the time, but as I understand it makes it difficult for modern Koreans to read. However, when I was researching the origins of the double arc-hand block, I noticed the pictures for Sam-Il looked different than the modern version. Curious about the instructions, I ran the instructions for Sam-Il -- as well as Hwa-Rang, Choong-Moo, and Ul-Ji -- through Google translate. I found some surprising things.

I know online translation tools may be inaccurate, but the text is substantiated by pictures in some cases. Here is what I found. 

Hwa-Rang and Ul-Ji are mostly the same

 

Unfortunately there are some pages missing from the pdf, so we only have instructions for Hwa-Rang starting at move 11. However, it appears to be mostly the same as the modern version [see note], except for a couple differences in stances. I'm not certain where the roundhouse kicks are meant to be aimed, since the floor pattern is on a missing page, but they aren't aimed forward. In modern Hwa-Rang they are officially aimed at 45-degrees.

Ul-Ji is also mostly the same, although a couple front snap kicks were originally side piercing kicks in the 1959 version. Also, the palm upward blocks seems to not have been created yet. Step 38 of Ul-Ji is instead a "middle inward block" with the palm heel. 

 

In this section of Ul-Ji, a side piercing kick was originally used

 

[Note]  There is a difference in moves 5-7 between the 1965 and modern versions of Hwa-Rang, but unfortunately the pages for these movements in the 1959 book are missing.

1959 Choong-Moo

Choong-Moo has some noticeable changes

 

Choong-Moo has more noticeable changes, including:

There are no roundhouse kicks (aka turning kicks) in the pattern. It seems these were added in later. Roundhouse kicks do not appear in any karate kata, so the decision to put them into Hwa-Rang, the first TKD form, was intentional. It seems they were later added to Choong-Moo as well, but not in the original version. 

The supported middle spearhand thrust was originally an upset spearhand thrust. I've long suspected steps 22-23 of Choong-Moo represent a shoulder throw. An upset spearhand (palm faces up) may be use to reach under an opponent's armpit. But it seems this was changed to a more familiar movement.

Only one side kick before the turn into the X-knifehand block. Because of this, you end up with your right leg back in the 1959 version, whereas in modern Choong-Moo you perform two kicks and end up in a left back stance

No twin palm upward block After the X-knifehand block, you step forward into a rising block and that's the final movement. As with Ul-Ji, the palm upward block may not have been invented yet.

Sam-Il was significantly revised

 

That brings us to Sam-Il, which would have been more recently created along with Woo-Nam. Between 1959 and 1965 several changes were made, especially in the second half of the pattern. Listed all of them would be tedious, but here are some highlights.

Move 11 of Sam-Il (1959)

Step 5, the lunge punch, was in a "low stance" sliding forward. A low stance is just like a front stance but wider and low. The slide was dropped in later versions.

Step 11, the double arc-hand block, was originally a combined rising knifehand block and palm-heel strike.

It seems the double arc-hand block was not yet conceived as a distinct movement. The next few steps also differ: you step forward into a reverse palm heel strike instead of a reverse punch. (Yes, you strike with a left palm heel twice in a row). Then there isn't any turn into a twin low punch; instead you step forward again into the reverse-knifehand (ridgehand) guarding block.

This actually caused me to rethink this set. So move 12 was originally a palm-heel strike, not a reverse punch? Why? That movement is pretty rare in the ITF patterns. And the fact that you step forward into the reverse-knifehand block (which is actually described as a strike in 1959 with the rear hand guarding the chest) indicates it's probably not picking up the opponent's leg as I guessed.

Is this a strike or a block? The fact that its name has changed means it's probably neither.

After the 360-degree spin, you land in a different movement. In modern Sam-Il you land in a knifehand guarding block, same as Choong-Moo. In 1959 Sam-Il you landed in a R. front stance high backfist strike with the left wrist under the right elbow.

The diagonal stance hand motions has changed, as well as the footwork

1959 version (left) and modern version (right) 

After the elbow strike, you step backwards a little to form the L. diagonal stance, and perform what looks like a modern angle punch with your left arm (though the text mentions the right rear elbow strike is primary). In the modern version, you step forward and perform a rear strike with your left elbow.

The last third of Sam-Il diverges from the modern version

Here the movements diverge. You perform many of the same ones as in modern Sam-Il, but in a different order. The one that perplexed me the most is the order of the covered punch and the back stance low block is switched.

1959 (top) vs 1965 version (bottom)

In the 1959 version, you perform the punch first, then step forward and perform a low block with the same arm, still keeping the reaction hand high near the armpit. In the modern version we perform the low block and then the punch without changing stance.

Both of these movements have unusual instructions for the secondary hand, but the applications for the 1959 and 1965 versions cannot be the same. 

 

Grasping your right wrist appears a second time. Step 3, where you perform a right knifehand block and grab your right wrist with your left fingers, occurs a second time in 1959 Sam-Il but in a cat stance, with different following moves.  

No palm upward block. Finally, I have to note there is no palm upward block in 1959 Sam-Il either.

What About Woo-Nam?

 

Pattern Woo-Nam was abandoned by 1965, but most of its material was reworked into the first two-thirds of Choong-Jang. If you compare this performance of Woo-Nam to Choong-Jang, you'll see the sequences were also significantly revised. 

Conclusion

 

Why the revisions?

It's important to note that the sequences in TKD forms are not merely karate sequences reordered around. While sequences from karate kata are sampled, they are often altered, and most TKD sequences in the higher patterns are original. The creators of TKD patterns did think about the movements and what they might be used for, and some of the revisions reflect logical changes. To give a simple example, in 1965 Tong-Il's opening two moves you step back once. In modern Tong-Il you step back twice. This it to make the underlying application (escaping a double grab) more effective.

However, not all the the revisions were application focused. Two roundhouse kicks were added to Choong-Moo, but in my opinion they were not required to make the underlying applications work. It seems there was a desire to add roundhouse kicks to more patterns since it's a staple of sparring but not in any karate kata.

There was also some movement simplification going on. The combined knifehand rising block and palm strike in Sam-Il became a double arc-hand block, as did a combined rising block and middle block in Bassai. Similar-looking movements were merged together. This is part of the standard karate and TKD training method of practicing basic movements with many underlying applications, but it does remove some of the nuance inside patterns.