https://www.ragandbone.ca/PDFs/Miyat...logue%2087.pdf
Miyata Team: 54cm frame has 54cm top tube; 60cm frame has 56cm top tube
https://web.archive.org/web/20011218...02_veloce.html
Bianchi Veloce: 55cm frame has 55.5cm top tube; 61cm frame has 58.5cm top tube; 63cm frame has 59.5cm top tube
http://www.vintage-trek.com/Trek-Fis...d/1987trek.pdf
Trek 560: 55.9cm frame has 56cm top tube; 63.5cm frame has 58.5 top tube
http://velobase.com/Resource_Tools/D...anasonic91.pdf
Panasonic 5000: 56cm frame has 55.2cm top tube; 63cm frame has 58cm tt
https://masibikes.com/collections/cl...ssico-frameset
Masi Grand Criterium: 54cm frame has 54 cm tt; 63cm frame 59cm tt

It seems like ~55cm frames tend to be square. Above 55cm the top tubes start to be shorter than the seat tubes. Below 55cm the seattubes are typically longer than the top tubes.