Well for the BWD files in the RMG (Ready-Made-Groups) directory, I already knew in a way that was where the randomized structures came from. But could this hold the key that may prevent Mercenaries skirmish missions from sucking???? I will try my luck at new self-made RMGs using Ed Wong's Mercsedit3D.
This is a list of BWD files I captured a while back while running a Mercs instant action mission on dosbox - some of the files are verbatim copies of files in the RMG directory (just renamed), the rest appear to be generated by the shell (including some, such as briefing and campaign files, that aren't actually used):
EN01STAR.BWD -> Randomly generated by shell?
EN02STAR.BWD -> Randomly generated by shell?
EN03STAR.BWD -> Randomly generated by shell?
EN04STAR.BWD -> Randomly generated by shell?
EN05STAR.BWD -> Randomly generated by shell?
MIS5ARE1.BWD -> Copy of RMG/DRPSHP3.BWD
MIS8ARE1.BWD -> Copy of RMG/PUMPSTN3.BWD
RAN0BRF1.BWD -> Generated by shell? \
RAN0DBFF.BWD -> Generated by shell? >-> Not actually used methinks.
RAN0DBFS.BWD -> Generated by shell? /
RAN0SCN1.BWD -> Copy of RMG/MIS8SCN1.BWD
RANDNAV1.BWD -> Randomly generated by shell?
RANDWLD1.BWD -> Randomly generated by shell? (includes generated files, files from RMG and files from PRJ)
RND0CAM1.BWD -> Generated by shell? Appears to be a dummy file.
USERSTAR.BWD -> Generated by shell.
I would guess the shell randomly picks some scenery from RMG, renames it and then generates RANDWLD1.BWD to include them (it also includes some MIS*.BWD files from the PRJ file). Anyhow, hope this helps a little with your investigations