In history.xml you can find the correct history of a game.
For Mortal Kombat, we can find the "original" game is: Mortal Kombat (rev 1.0 08/09/92) (Midway 1992) [ROM set: mkla1]
It is NOT the parent which is called "original" in MAMEUI
PROTO 4.0 (July 14, 1992):
* Prototype version.
* You cannot play as the same character.
* Menu won't allow cursors to pass each other in 2-player selection.
* Sub-Zero has new corner infinite (ex. uppercut, freeze and repeat)
* Sub-Zero has faster recovery after slide and can go straight into sweep for most instances
* Sub-Zero can freeze opponent in air for 'Finish Him/Her' as he's falling from uppercut, and do fatality in air and body will fall to ground frozen
* Liu Kang can do Flying Kick when you do a HK first in air than F, F HK
* Raiden can now do Torpedo after doing a jumping kick for more combo possibilities
PROTO 8.0 (July 21, 1992):
* Prototype version.
PROTO 9.0 (July 28, 1992):
* Prototype version.
REV. 1.0 (August 9, 1992):
* First official release of Mortal Kombat.
* In a 2-player game, both players could not choose the same character.
* Liu Kang had Uppercut - Flying Kick Combo.
REV. 2.0 (August 9, 1992):
* Both players could choose the same character.
* New Shang Tsung death animation added.
* Merchandise promo added.
* More blood added.
REV. 3.0 (August 31, 1992):
* Computer intelligence increased.
* Reptile added.
* Comic book offer is a switch setting.
REV. 4.0 (September 28, 1992):
* Reptile clues added (shadows on moon, see Tips and Tricks section).
* Sonya and Kano could fight Reptile.
* Block allowed during fatality.
* Goro's theme played during all Endurance rounds.
REV. 4.0 [T-Unit] (February 11, 1993):
* Runs on the newer Midway T Unit hardware, the same hardware as Mortal Kombat II
REV. 5.0 [T-Unit] (March 19, 1993):
* Bug fix release.