I am close to buying a 48cm Vitus 979. Not sure of the exact year but it has the rear collar bolt on the seat tube not the Grub screw. Here's the concern; the seat tube measures 48cm. All other 48cm bikes I've seen and all geometry numbers I've seen for this frame size indicate a 53cm top tube. However, this owner swears it is 50.5cm. He is an honest guy, who has been in the bike industry for quite a while and has been a bike designer....so I think he knows how to measure a TT. He thinks it could have been some sort of limited run. Kinda hard to believe but possible? Also, there is no frame size stamped anywhere on the bike even though I have seen it on most other Vitus frames. I've seen photos and the bike looks clean and untouched.

Anyone have any opinions?