The GRS
Hmm, it is said about the Great Red Spot that it had been discovered more than 300 years ago.
That was some time after Galileo (I'm sure Galileo would never have discovered it with his refractor!).
So, perhaps, the GRS was discovered only once the instruments were powerful enough to detect it. Meaning, it was there for a much much much longer time!
It is VERY difficult to see the GRS even when Jupiter is a good sized disk on the eyepiece: it's because the contrast between the general color of Jupiter and the GRS isn't very important.
The GRS is still very mysterious.
Raoul