Age of masters


Seeing new releases using re-masters which to me means they use the original 40+ year old master and twiddle some knobs.

Do 40+ year old masters still have viable iron oxide?  Would high frequencies suffer? Or do I misunderstand re-mastering?
128x128ibmjunkman
Mercury is about to re-release its entire classical catalog.  Some of the masters are as much as 70 years old and still sound great.
I read that Mercury is making it all available to streaming services. Nice of them...
Many record labels transferred their analogue libraries to digital to preserve the master.