I believe the sample version of this game was dumped in 2016. This would have been used as a test version, to allow players to try out the game in arcades before the official release. There are a lot of gameplay differences, however I'm no expert on this subject. Certain moves have different priorities in the sample, and certain characters are better -from what I've read E. Honda was much stronger in the sample version, and was heavily nerfed to the point of being bottom tier in the final version.

The non-gameplay differences are minor. One thing of note is that the voice clips aren't working that well in the sample version, many characters make generic grunts instead of calling out their move names, despite the voice clips being in the sound test. These were all fixed up for the final game.

Sample	Final
The sample version makes it clear what it is on boot-up.

Sample	Final
The title screen has a different background color.

Sample	Final
The single player mode only has 8 stages to beat in the sample, in the final there are 10. The preview also lacks any dialogue before certain fights, in the final version there is usually dialogue for the fifth, ninth and tenth stages. The ending sequences aren't in place yet in the sample, beating the eighth opponent results in a game over screen.

Sample	Final
All of the characters who were in the previous game are still using their Alpha 2 win quotes in the sample. In the final version, these win quotes were all removed, and a new set of win quotes were added for each returning character.

Sample	Final
Characters who made their debut in Alpha 3 have their win quotes. Some match the final version, whilst. some were just minor text changes, like this one of Karin's...

Sample	Final
...whilst others were completely altered due to them not making any sense.

Sample	Final
Special mention has to go to Cammy's win quotes, which were all re-written for the final version.

Cammy's cannon spike move has her say something different in the sample. To me it sounds like "chauf kick!" but it might be an Engrishy version of "thrust kick!". In the final it's "cannon spike!" I think that originally, it was intended for the American version of Alpha 3 to have some of Cammy's move names changed, as had been the case for Super Street Fighter II. But this was ditched in the end. However, the "chauf kick" can still be heard in the final game's sound test, it just doesn't get used.
Sample	Final

Cammy's spiral arrow move also has a different voice clip. In the sample, she just says "cannon". In the final, she says "spiral arrow!". This move had different names depending on the region in Super Street Fighter II. In Japan, it was "spiral arrow", but in America it was "cannon drill". It seems that was the plan for Alpha 3, but they scrapped this in the end. In the final version of the game, this voice clip was updated in the sound test, so she says "cannon drill". But it still goes unused.
Sample	Final

Sample	Final
By using cheats, it's possible to play as the hidden characters. Juli and Juni have incomplete move sets in the sample version, at this point, they have all of Cammy's special moves and supers. In the final version, they each had a few unique moves of their own. In the above example, Juli's QCF+K move is a spiral arrow in the sample, but a flying kick in the final version.

By using emulator cheats, you can force the sample version to have its region changed to Japan. Whilst the title screen still displays the Alpha 3 name, the usual character names are changed (eg Gouki instead of Akuma) and there are a couple of other differences. The above mentioned Cammy voice clip differences don't apply to the Japanese test version, she has her final version voice clips for her moves.

Location test	Final
This Japanese version of the sample refers to itself as a location test version on boot up.

Location test	Final
There's a problem with the win quotes where the kanji goes off the screen, the final version fixed this.