Question on CPF3281 and "sharing of format xyzf with file yxzp in library abc could not be established"

I have been asked to restore files from 1987 - 1992.

These files were saved via a home grown process, where the files were created with filename + twodigit year in a library called YEARnn at the end of each year.

These files were then saved onto 8mm tapes.

A 3rd party converted the tapes for us from 8mm to LTO 7.

But when I try to restore the needed files, I get CPF3281:
Message . . . . : New format OEI020F created for file OEI020P91.
Cause . . . . . : File OEI020P91 was restored into library YEAR91. However,
a new format OEI020F was created for the file because sharing of format
OEI020F with file OEI020P in library PRDDTA1 could not be established again.
The possible reasons are:
1) File OEI020P in library PRDDTA1 using format OEI020F with a correct
format level identifier does not exist.
2) File OEI020P in library YEAR91 using format OEI020F with a correct
format level identifier does not exist.
3) The allocated length of a variable length field in one file does not
match that of the other file.
4) One of the files has an identity column and the other file does not, or
the identity column or an identity column attribute in one file does not
match that of the other file.
5) One of the files has a row change timestamp and the other file does
not, or the row change timestamp column or row change timestamp attribute in
one file does not match that of the other file.

This falls over into CPF3729, Error decompressing file *NONE.

My intro to the AS400/iSeries/i world began in 2000, so "sharing of format" isn't something I have ever seen before. Is there a workaround for this? We no longer have saves of the original PRDDTA1 files for those years. The only saves I have will be from years later when the formats of the underlying files are unlikely to be the same. I know that for the key file I need, the DDS source I do have was generated over a decade later by a 3rd party code/file generator.
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