The girder 'finger' as I call it, can be replicated in any version of MAME going all the way back to 2001 (the earliest version I could get running on my computer). Here's the breakdown on how it comes up and what settings are needed to see it:
MAME 0.56 to 0.84: Cheats enabled, CPU0 set to 99%. Dates from November 2001 to July 2004
MAME 0.85 to 0.115: Cheats enabled, refresh rate set to 60.600 (approximate match of arcade version). Instead of changing the refresh rate, the original trick of setting CPU0 to 99% still works in these versions. Dates from August 2004 to May 2007.
MAME 0.116: Shows up by new default of arcade refresh rate, but shows a blue background. June 2007
MAME 0.117: Shows up by default of arcade refresh rate, and is back to showing a black background. July 2007
And we can stop there.
My suspicion is that MAME 0.85 (August 2004) or later was used, because setting the refresh rate to match the arcade's 60.6 Hz indicates technical savvy in an attempt to deceive the public. Even so, the fact that the 'finger' can be replicated many years before Billy's tapes surfaced means his defenders have no escape from that evidence. All they can do now is pray that Carlos can finagle a video to show the same thing happening on real hardware. If Carlos dares to cross the line into shenanigans like that, he won't be able to provide instructions so that anyone else can replicate it.