I can fail 50's 100 times too, just not with a valid throw.
I do believe 51 is a good WR, because it requires a pretty perfect run (Good lines, throw from far away and warp). I have never seen a 50 fail myself playing around tops 10 hours going for 51, even when trying to throw the mine from further away.
50 would be an insane WR on Surface 2, and if Goose doesn't get it sometime soon, 51 will stay WR for quite some time. It will probably require a boost.