MARP players aren't constrained to use TG settings except in a few cases where the games degenerate into mind-numbing marathons. Sometimes the games are inherently harder in MAME than they are in the arcades, Star Wars is a good example, so even though Star Wars is marathonable, no one has marathoned it in MAME. Back in MAME 30 when INPs first made an appearance lots of games didn't read the dip switches at all. Also sometimes the dip switches don't do anything, even in the original arcade version. I spend years trying to figure out what the dip switches did in Carnival, after reading the manual to the game I now know they don't do anything.(posted 8483 days ago)In some other games, it's not very clear what exactly the dip switches do. The original TG list of settings was based on the arcade games up to 1985, so naturally games after this were not included. I've extended that list as best I could. Of course there are tons of games I've never played, and to rigorous test every game to see if the dip switches actually do what they do in the arcade version seems an almost impossible task. Certainly it will be years yet before all the dip switches are well tested.
I'm aware that the MAME emulation isn't perfect. The controls aren't going to be as good for one thing. Not all circuitry is emulated either, in the pac games the watch dog timer isn't emulated. I'm sure there are other games aside from Ghouls and Ghosts which didn't get all the dip switches right.
All I can say with absolute certainty is that all the games I own have the emulation and dip switches correct. I can easily compare that Blockout, Joust, Ataxx, SF2 CE, SF2 Hyperfighting and Dig Dug all are emulated correctly. In the case of Blockout the dip switches were all labeled "unknown" at one point, and I pointed out that certain dip switches were used, and other ones were not, so that information was added. But in a lot of the cases the owners of the games aren't telling the MAME Dev people about which games have the dip switches wrong.
Generally the situation has got a _lot_ better since the days of MAME version 30, but it's not perfect. I expect MAME will keep improving. And the TG settings for MAME are not completely inflexible. If someone emailed me saying "I didn't follow TG settings because the dips don't work in MAME" I'd definitely still accept the score. In the future if the dips were corrected I can always make 2 categories for that game... Default and Tournament.