How to revert back or undo after changing the schema for a form - submitted data does not display. v4

version 4.1.11.

Recently made a change to the schema associated with a form - changed data type from int to string.  After uploading the changed schema, all previously submitted forms now appear empty and we see the following errors:

INFO: 15:13:35,129  WARN XMLImporter:412 - DocumentType not found for element http://www.frevvo.com/schemas/_Flg8OsNtEeSEyoJqOoFqHQ#form
15:13:35,129  WARN XMLImporter:432 - Ignoring unexpected element {}form when parsing xml document
15:13:35,129  WARN XMLImporter:412 - DocumentType not found for element #tDocType
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The DocumentType not found errors continue on.  After trying to revert back to previous data type and re-uploading the schema, we still can't get any submitted forms to display their data.

Anyone ever deal with an issue like this before - any suggestions for how to manually fix this or revert the proper way?  Clearly something got out of synch, but we aren't sure where to start looking.