I don’t think the DPE ever signed my logbook for any of my initial rides. It just went in my logbook as PIC and a notation in the comments section like you stated that you have. It’s never been an issue and was never even mentioned in any interview, Frontier included.

There’s no regulation that says the DPE has to sign your logbook. It’s not like documenting the instructor if you received dual instruction. The DPE signature on your temporary at the time is their documentation.

If you’re really concerned about it request your full airman file from the FAA (and bring it with you to the interview). It will have a copy of every written test result, every 8710 you’ve ever filed, every temporary certificate, notice of disapproval, and medical you’ve ever had. A quick comparison of the date your temporary for that particular temp certificate was issued to the date in your logbook would be proof enough that the entry your claiming to be your Checkride was, in fact, your Checkride. Remember, in the interview it’s less about your logbook and more about responsibility and accuracy. They want to see that you’ve done the legwork and took responsibility for accurate documentation as well as problem solved to prove any inaccuracies.