I was not able to find a specific reference, but I have recently read that in some cases if it is not possible to determine whether an ordinance was done (and perhaps when/where/etc.) that ordinance may need to be done again.
Perhaps you were referring to this section of the Handbook:
GHB 38.2.6 Validating or Ratifying Ordinances, which describes the process for resolving issues with ordinance records.
When I click on the ordinances tab for the YM on LCR I see a message "Aaronic Priesthood offices are not displayed for members holding the Melchizedek Priesthood."
If the YM has already been ordained an Elder, then indeed you'll see this message. And for Aaronic Priesthood holders, it only displays the most-recent A.P. office. So if you're looking to update a previous A.P. ordination, calling SLC is probably the only recourse.