@kraftwerkturbo It depends.
I purchased a case (10 reels) of Maxell 35-180 UD tape in 1981. A few years later, I purchased two cases (20 reels) of "Ampex GM-3600 Grand Master Professional Recording Tape."
From the mid 90’s to the mid 2000's, my R2R sat mostly unused, but I would play a reel on rare occasions. Around the mid 2000’s, I noticed my Ampex tapes started to sound muddy and were leaving a lot of residue on the tape heads, pinch rollers, and transport mechanism so I had to stop using them (because they sounded like crap).
My Maxell reels are still playing just fine.