Man i am really confused.  So my GS is titled a 98, mfg date is 5/97.

I searched very thoroughly for a front sprocket that would fit.   I ordered a JT 516-15, wouldn't fit, the shaft hole is too small on the sprocket.  So I am thinking man maybe I needed one without the shoulder, so I order JT 565-15.  Both of these are supposed to fit my bike. Both the spline shaft hole is too small to fit.

I cleaned the sprocket on my bike off and there are no markings what so ever on it to tell me what to order.

Anyone else run into this problem?

Can you see any obvious differences between the new and old sprockets? Could be that the splines have worn slightly on the shaft and formed raised edges making it difficult for the new sprocket to slide on. A few light licks with a decent file will remove them. Failing this it can only be one of three things. Either you have ordered or been sent the wrong sprockets, the sprockets are sub-standard or someone has in the past fitted a non-standard output shaft to your bike.
The standard output shaft has a 13 spline pattern. 21.6mm rib to rib, 25.0mm trough to trough.

The JTF516 sprockets should fit all 94 and later GS500 models.  I have one here in my hand that's marked JTF516-16 to put on my 02 GS along with a new chain in a few days.  Hope it fits.   

I will count the output shaft splines...never thought of that in my fit of rage.

Putting my new JT516 front sprocket on with the chain out of the way was a little difficult, putting it on with a properly adjusted chain around it was very difficult but doable.  Once started on the shaft it has a nice close sliding fit.  I like it that way.