I am about to learn to find the general correct turnover and rolloff curves
for US and European 78 rpm records.
So far I have learned:

US 78 rpm records:
Pre. 1938: turnover 500 (RIIA), rolloff FLAT
After 1938: turnover 500 (RIIA), rolloff -5

European 78 rpm records:
Pre 1938: turnover 300, rolloff FLAT
After 1938, turnover 300, rolloff -5

Can anybody share their experiences within this matter, please?

All the best
Jan Myren