Affects Version/s: 1.6.76 (java), 2.0.1003 (Windows), 1.6.89 (java), 2.0.1049 (Windows), 2.1.1216 (Windows) / 2.1.1217 (Mac OS) / 2.1.1218 (Linux)
Fix Version/s: None
Environment:OS: Windows 10
Java version: 8
NOTE: THIS IS NOT AN ISSUE WITH THE OLD VERSION OF THE GAME SPECIFICIALLY. THIS IS BECAUSE THE VERSION OF THE GAME IN QUESTION IS MISLABELLED ON THE MOJANG SERVERS AND ALSO THE LAUNCHER AS A RESULT. This ticket may be moved the the WEB project if more applicable.
The Minecraft Launcher claims to have the version "a1.2.1" available, but it is a copy of "a1.2.1_01". Upon inspection of the .json files, both "a1.2.1.jar" and "a1.2.1_01.jar" contain identical SHA-1 hashes and file size under the "downloads" section. I also calculated the SHA-256 hash with an external utility, and both .jar files have identical hashes. Both versions display "Minecraft Alpha v1.2.1_01" ingame, which suggests that both versions are in fact "a1.2.1_01", despite one of them claiming to be "a1.2.1".
This strongly suggests that the "a1.2.1" version listed in the launcher is a duplicate of "a1.2.1_01", and should be removed from the launcher, since there is no point in having two copies of the same version listed in the launcher.
Attatched images are the following: brp1.png compares the .json of "a1.2.1" and "a1.2.1_01", showing the identical SHA-1 hash of the .jr files within the .json.
brp2.png compares the SHA-256 hash of both of the "a1.2.1" and "a1.2.1_01" .jar files using an external utility (7zip). As you can see, the hashes are identical, which strongly suggests that both "a1.2.1.jar" and "a1.2.1_01.jar" are identical.
brp3.png shows "a1.2.1" running ingame, displaying "Minecraft Alpha v1.2.1_01". brp4.png shows "a1.2.1_01" running ingame, displaying the same text in the upper left corner.