As part of my own fundamental research undertaken to launch Reel to Reel Warehouse, I stumbled upon this excellent research paper by By Mike Casey, Associate Director for Recording Services at Archives of Traditional Music / Indiana University. This is a 70 page document with a ton of great information on identifying tapes for archiving and preservation purposes. I suggest you download it and keep it as a reference guide.
Among the many points made in the paper, it is clear that preservationists do not see long term issues with most reel to reel media (at least the good stock) as long as it is kept in the proper environments. It’s one more reason to be confident that you can use old tapes for your own applications without fear they will self destruct or ruin your machine – as long as it is the right formulation!
Another well known paper used for further technical analysis of tape degradation is from Richard Hess – here is describes many of the terms used in this website: