I understand that these are the same tape. -PRR is the new part number and -PRL is the obsolete part number. -PRR part number has been around for quite awhile. Does that mean if I see -PRL tape for sale they have been sitting on the shelf for years and not as fresh as the -PRR and avoid them?

Yes same tape .. Sony PRR (6 pack) and PRL (10 pack) and PR (5 pack) refers to various Sony bulk packaging for marketing purposes .. some are being discontinued.

However the tape itself has a life of about 30yrs .. go ahead and welcome to the forum :)

Cheers.