I think that this describes fairly accurately the process of renaming.
If there is no data in the field ORIGYEAR but you need that then any attempt to use non-existent data will lead to undesirable results.
I am not sure who is supposed to carry that out what
and I am also not sure what the task would be.
So far you present only very vague information about you do so that I do not see me in a position to help to find the root cause of the ORIGYEAR tag confusion.
It would help, though, if you told us
what action for which field you use,
what the format string looks like,
what the data for the relevant fields looks like and
with which property you start and how the property should look like in the end.
Or you test your format string in one of the converters, Tag-Filename for the _FILENAME or Tag-Tag for _DIRECTORY.