If you have used the incorrect oil filter for a few years and you have noticed no untoward effect on your engine then you have nothing to worry about. I have a new oil filter left over from my 2001 gen1 1000 and when I bought a new filter for my 2007 FZ1 the only difference was the length of the filter itself.
It looks like the -50 is simply an updated number for the -20, and the two filters are the same.
It looks like the -50 is simply an updated number for the -20, and the two filters are the same.