Trying to put 73057 into 16 bits; it will result 7521 at receiving side.
The problem is with player culture value that is sum of all history and culture. National history value is not similar problem, as it doesn't even include city level history.
The player culture value is part of the protocol only beginning from S3_0. So leaving S2_6 target out.
Freeciv version 3.1.90-dev gui-gtk-3.22 Built from git 20210221 The Value 73057 are the "Culture" score.