Bulk assign contribution page based on contribution type?
Have you tried exporting those member dues contributions (including their contribution IDs as well as their Civi contact IDs), adding a column for contribution page ID, and importing that information back in as an update of the existing contributions?  If you've not tried that, it might be worth testing with a small subset of those member payments to see if you get the results you expect as far as updating the information.

Lesley