Do 1965 dated 90% silver coins exist. Yes. Are they INCREDIBLY rare? Yes.
It seems like a perennial topic on this board that someone edge searching has found a silver 1965 dime/quarter or a 40% silver 1971 half, and it ends up being just plated or just a weird anomaly.
You've got to weigh the coin to find out. The edge checking method is not completely foolproof, even some modern clad coins end up being punched weird so that they have nearly no copper showing, if the weight is the same (or just slightly off) there is no error.