It seems my Kindle does in fact use all 50 screen savers.
I initially put my Kindle to sleep, wrote down the screen saver that popped up, woke it up, put it back to sleep, recorded that screen saver....etc....etc. After 36 screen savers it repeated the 1st 2 on my list so I thought it was repeating the same 36 screen savers. But upon further review, after repeating the 1st 2, it proceeded to continue through the remaining 14 screen savers.
So the Kindle can handle at least 50 screen savers, and I would imagine it should probably handle much more than that.