There are several versions of the '33s with variations in the shape of the hole for the brace for the main front fender bracket and the size of the convex bulge, but they all have that small circular indentation that deuce lover refers to. You can use a '34 fender with a '33 inner panel, but you cannot use a '33 fender on a '34 inner panel without reworking the lip on the fender.
The other fundamental difference between the '33 and '34 inner fenders is the lower edge reflecting the inside-the-frame mounting of the front shock absorber on a '33 and the outside-the-frame mounting on a '34.