While the variations are subtle, they consistently appear as such and I'll explain them as follows, using the labled scan above. (Note, the image at the center is all four chips as viewed from the edge, showing the side insert dashes.)

Chips 1 and 2 are the more recent "BJ" stamped versions. They differ in the shade of tan used for the inserts and mold patterns. While the difference is subtle, it stands out when you have a stack of these chips and they can easily be sorted by the two different shades. Chip 1 is lighter than chip 2. I suspect that a re-order explains the difference.

Chips 3 and 4 are the earlier issue of this chip, and they all appear in one of two different edge inserts styles, a thin line and a thick line. Again, a subtle difference, but easily seen in a stack and easily sorted by that difference. Chip 4 is the thin version and chip 3 is the other. (Note, chips 1, 2 and 3 all have the same size edge inserts, which may indicate that chip 4 was the earliest version of the 1st issue. Not absolute, but perhaps.)

Well, enjoy the hunt!