The dropouts were changed on the Titanium frames in 1990 to match the new afterburner rear stays of the steel Marin range, and this dropout was carried through to the mid 90's.
At no point did Marin use 4 digit numbers on a dropout to stamp their steel frames, that was only the Lynskey bros. at Litespeed who did that.
Steel (with the eyelet)...
I've already posted a 1990/1 picture
I don't have a 1992/3 picture to hand, but they are different again.
pre 1990...
1994 to 1996 (really poor picture)...
1999 (now made by Ti Sports)...
It's worth noting that I was once told that Litespeed would often use whatever dropouts they had to hand in order to finish a batch, so it is not uncommon for some old dropouts to be used up on later models, hence the haziness on identifying exact model years from the dropout alone.
The headset size increases from 1 inch to 1 1/8th in 1991 also, which is a better means of identifying them from this period.