Hard to say. Size is a thing the manufacturer determines and many don't size their bike by the same methods. They only generally are the length of the seat tube on old bikes. And even then some mfrs went to the very top of the seat tube, some to the top of the top tube and others to the center of the top tube and maybe a few other ways.

Sloping top tubes have added a few more ways to figuring out a size too. Now it's common to draw a imaginary horizontal line from the somewhere around the top of the head tube and extend it to the extended center line from the seat tube and measure from that intersection to the BB center. But only some do that and others do something else.

So if you are buying a bike. Just know what measurements you need and don't worry so much if the owner says it's one thing and you think it's another. Especially if you are only 2 cm off.