Hi PhilMH. I am fairly sure this was a very "budget friendly" release at the time I purchased it (late 90's), mayby under $10. Looking at Discogs the bracketed number seems to be mostly confined to CCR releases, though I did find a Frank Zappa cd "D20193" from 1998 and a John Fogerty cd "D20169" from 1997. The bracketed D2**** number does appear to be a catalogue number of some description even if short lived / discontinued.
Although this version is copyrighted 1997, this album's first Australian CD issue under this same catalogue number was on 26th March 1990, see Discogs. I don't know for sure where the D 20181 number in brackets comes from - usually with Festival, numbers in brackets signify either the original overseas catalogue number, or a previous Australian catalogue number, but there is no trace of such a number in Platterlog. I think the 20000 series was probably a mid-price reissue series, perhaps even a continuation of the 19000 mid-price reissues, so perhaps Festival first considered reissuing this at mid-price before putting it out at full price, using the original Australian LP catalogue number with the prefix suitably changed from L to D. Whatever the reason, that bracketed number is not truly a "current" catalogue number.