Welp, make that a corrupted CD!
Having done a file compare between the file on the CD and the resource.aud from the GOG version, there is a difference, but only in that file, everything else on the CD matches GOG's version. The difference runs entirely from 018C3800 to 018C3FFF. Exactly 2048 bytes, which is too round a binary number to be a coincidence, and it is the sector size of a CD-ROM. So there is probably a single corrupt sector on my CD (or the master it was built from)!
In my CD's version, the 303 consecutive bytes at offset 018C3ED1..018C3FFF all have value FF, which is obviously wrong. I'll just use the GOG copy then, and apply the patch to that!