The Gardnier/Orchestre Revolutionnaire et Romantique set of the Beethoven Symphonies is now 25 years old. They were recorded for "Archiv", DGG's label for "Early Music" [Bach mostly, to start with] since the 1950's. The 1990's were the time HIPP started being applied to classical and romantic era composers. There were earlier examples, but Historically Informed Performances of Beethoven became a "thing" in the early 1990's. HIP Baroque as the norm has been going on longer than that.
I'd say that issues with deterioration of audio recording are all over the place. Analog tape can deteriorate from bad storage, wear obviously applies to the disc formats. And then there's CD rot, like that Hannover Band set of the Beethoven Symphonies that I found [the first complete Historically Informed set], all the silver coating on the discs turned to grey, rendering the discs unplayable. Storage of digital sources might hold up better over time, but that will require a lot of back-ups of digital data. Hard drives wear out, SSDs can lose all data catastrophically, lord knows how long Micro SDs hold up [I've got one filled with 500gb of music, another, redundant, Micro SD with 400gb.] For me, the greater concern is that audio discs, LPs, 78's and so on, have the sound quality go downhill right from the get-go, due to the groove slowing down as the stylus gets to the end of a side, something that cannot be worked around. It doesn't matter how much money gets poured into playback gear or discs, the sound quality will go downhill on an LP as it plays.
Interesting choice, Beethoven's 9th. The first recording I heard [50 years ago] was Bruno Walter's New York Philharmonic recording, taken from two sessions, a 1949 session and one made a few years later, all on a single LP. I think that was the first complete Ninth on LP. The adagio had to be split in two over two sides, both sides were over 30 minutes in length. The sound wasn't very good in the first place, but it got much worse by the end of the choral finale. Didn't hear a properly dynamic recording of the 9th's scherzo until Solti's recording with the Chicago Symphony Orchestra of the 1970's, where the symphony was spread across 4 sides with the scherzo having a side of it's own. Of course, by the time these recordings made it to CD, the point was moot.