I think the transition to traditional twin stays took place around 96. They were still using the leftover Ti tubing from Somerville and building monostay frames in 95 at the Saratoga facility. Afaik FCC started to weld disc tabs on their bikes towards the end of their production in 99/00 before they closed shop. This could have been sent back to the factory for disc tab installation.
I have this frame in L. Its a special ride and a keeper for life. Manufacturers didn't make butted Ti tubes in the early 90s so FAT City used a lathe to do it. A time consuming costly process. Merlin experimented with chemicals to butt tubes but it was not effective, apparently. Pioneering bike technology at its finest, often copied and still not bettered even today.