AssemblyFileVersion Format and Limitation
It has to be the format of x.x.x.x and each x is a 16-bit number, therefore the max AssemblyFileVersion is 65535.65535.65535.65535
It’s a limitation of Windows, not .NET:
FILEVERSION: Binary version number for the file. The version consists of two 32-bit integers, defined by four 16-bit integers.