Maybe my sense of this is a little different.
Late 90's/very early 00's BN's had a thinner/faster neck profile.
At some point in the early 00's the pickups changed sources, similar but a little different sounding IME.
I thought the "crystal" finish replaced the thinner less durable nitro somewhere in 04-08.
Personally, having owned BN's from the late 90's, early 00's, mid 00's and late 2010's I really like the old ones. The thinner neck profile, the nitro which I thought resulted in a more resonant and open sound than the heavier albeit more protective newer finish. Im sure it varied a ton from bass to bass, but the MVP BN's that I have played and owned have been the earlier ones.