Aaaaah, so I'm guessing it's not a normal ROM thing, in as much as they all have it. Interesting and actually, a life saver (For my cocktail cabinet).
Every game in MAME offers a Video Option called "Cocktail", but that doesn't mean it will look or work exactly like the cocktail cab version of the game.
Many games had cocktail cab versions. Some did not.
You have to take it on a game-by-game basis.
In many cases you can get one of the six approaches mentioned above to work.
Does this also impact the controls? ie, designating one USB port for player one and another for player two?
This is an upright Space Invaders cab.
- Player inputs are left, right, and fire.

If you look at the MAME control inputs for Space Invaders, you see that there are P2 controls listed, but those are ignored when the cab type is configured to "upright".
- During a 2 player game on an upright cab configuration, the players take turns using P1's controls.
- During a 2 player game on a cocktail cab configuration, each player uses their own set of controls.
On the other hand, the MAME control inputs for Asteroids only show P1 controls because P1 and P2 controls shared inputs on J20 pins T, 14, S, 15, and 10 seen on pg 2 of the upright schematic
here and pg 5 of the cocktail schematic
here.
- This is also confirmed on the KLOV asteroids pinout
here. We know that this pinout applies to a cocktail because it shows pin 19 "INV X" which is only connected on a cocktail harness. It controls the P2 screen flipping as explained on pg 4 of the cocktail schematic linked above.
For cocktail setups like yours, in games like Asteroids that only have P1 control inputs you need to map the MAME P1 inputs to both P1 and P2 controls.
For example, in Asteroids you would map the Fire input to both Ctrl (P1B1) and A. (P2B1)
- Highlight the desired input.
- Press Enter.
- Press the P1 button. (Maps the input to that button.)
- Press Enter.
- Press the P2 button. (Maps the input to both buttons.)

Scott