Road bike sizing, is the seat tube, depending i believe on nationality played a big part on whether it was centre bottom bracket to top of seat tube or centre of lug.
The angles would be 73 parallel with a bit of variation depending on size. and the top tube was usually the same length as the seat tube, again with a bit of variation.
So it is that my Lemond Croix de Fer is a 57cm, and i believe the geometry gives me a top tube of 57.5mm, the seat tube a laid back 72.5 and a steep head angle of 73.5.
What has since happened is that compact frames came out, but the referral is to the seat tube, which happens to be the same as the top tube.