serialized_v23.dat has version 24 encoded in the header:
00000000: c2b4 0300 0018 0000 0001 0000 0010 0000 

serialized_v22.dat has version 23 encoded in the header:
00000000: c2ac 0300 0017 0000 0001 0000 0010 0000

serialized_v21.dat has version 21 encoded in the header:
00000000: c2b4 0300 0015 0000 0001 0000 0010 0000

serialized_v20.dat has version 20 encoded in the header:
00000000: c2a4 0300 0014 0000 0001 0000 0010 0000 

My understanding is that the serialized version should match the version in the filename, so we'll need to fix version 23 and version 22's dat. We should also update the test to assert that the versions are correct (which will require poking a small hole in page_state_serialization.h for testing).