What actually happens when you "remarry" a pkg?

Say you remarry a update.pkg to a game.pkg, what actually changes to allow it to no longer give an error? I'm probably wrong, but the only things I see different before and after a remarried pkg is:

Sc0\origin-deltainfo.dat : ___MISSING___...___________WORKING\2_patch_dump\
Image0\sce_discmap_patch.plt : MISMATCH
Sc0\param.sfo : MISMATCH
Sc0\pic0.dds : MISMATCH
Sc0\pic1.dds : MISMATCH
Sc0\playgo-chunk.dat : MISMATCH
Sc0\playgo-chunk.sha : MISMATCH

There could be more, but I'm...

What actually happens when you "remarry" a pkg?