Changes

Based on this logic, I think that the difference between a "parent document" and a "parent grant document" depends on whether the parent patent application has been granted. If the parent patent application is still pending (meaning the patent has not yet been granted yet) then I believe the reissue patent will store information about the parent patent under "parent document". However, if the parent patent application has been granted, then the information will be stored under "parent grant document". This seems like the most logical explanation, especially considered the path to any field related to "parent grant document" contains "parent document" as with the example below:

=====Fields=====