While I'm here, something that can be a problem with obtaining arcade ROMs in such a fashion is that it can be difficult to find the emulator version that correlates with the romset. I did try and parse Retroarch DAT files for the CRC of a particular romset but without much luck. Anyone tried something similar?

It's also possible to update your cores and break certain games. Retroarch does have 'snapshot' cores that remain at a fixed version (e.g Mame2010) but the main Mame/FBNeo cores are nightly builds. You might find you have a romset that's too new for the last snapshot core but not new enough for the nightly core so won't work. It's possible to grab older versions of cores from the RA buildserver but they only go back a couple of years.

As a specific example, Raiden Fighters from the Raiden Legacy collections is seemingly like this.

Haven't tried messing with any of that yet, but "goNCommand" along with https://github.com/farmerbb/RED-Project/wiki support almost everything there is to have on GOG and isn't already in a ready-to-use format.

Can't say I've had a lot of problems with that, but yes, some romsets are only compatible with certain snapshots of MAME. I think FBNeo has some older snapshots too (used to be called Final Burn Alpha, so it's lr-fbalpha2012), but I've found most romsets you can obtain on GOG are compabile with the nightly builds and rarely break. This has been the case for me in the last 2 years at least.

Some additional notes here, to whom it may concern:
- Broken Sword & Broken Sword 2 feature a variety of European editions (German, French, Italian, Spanish etc.)
- Lure of the Temptress also has several European editions (German, French, Spanish)
- Beneath a Steel Sky only features its English edition

For Lure of the Temptress/Beneath a Steel Sky, if you are running them with PUAE, remember to disable the WHDLoad utility, as the provided images need to boot straight from the their own volumes.

Raiden Fighters works well with what RetroPie dubs lr-mame2016 (IIRC it's MAME version 0.174). See attachment, it runs and plays just fine. Actually, all the other games in the pack have various issues fixed with lr-mame2016, such as missing in-game sound effects and music.