They weren't in a temperature-controlled environment, I'm afraid. Every single one that I have attempted to play, has been outright eaten by the cassette deck (and it's not a poor quality system).
I have a dual deck I have to take apart, another tape was eaten recently, and I threw my hands up in disgust. A lot of the radio show stuff I have is bootleg recordings from the station that was playing them originally; we'd take a boom box (all I remember is that the stupid thing took a LOT of "D" cells, and it weighed a ton) and those cassettes camping, and get all spooked up around the campfire after dark.
I'd guess some of those tapes have seen temps near 110F.