A Masi Measure 50cm will be very close to 48cm center to center, but Masi did not measure ctc for consumer marketing.
Colnago measured both ways! Some of the build cards for Eddy Merckx were center to top and some center to center- noted when done ctc.
I have A few Gios bikes, they are stamped center to top, top being top of the top tube, not including the seat lug extension.