Pretty sure its just a patch fix for the old version 0.74.
The real 0.75 was supposed to have a new character used in the game, but the 0.74 was needing a fix because of bugs with some of the gameplay and the tapes being bugged when playing them.
If you read the development log about the Electra system test, it was due to that topic that the game got updated, and named 0.75 Legacy indicating that its to fix the problems they had for the 0.74 version.
For what i can see from the legacy build, is that there is nothing new to it other then some bugs and the tapes being fixed.