For whatever reason, Estes didn't include the small balsa standoff on the die-cut balsa sheets.
This is a small launch lug standoff.
If you've never seen how die-cutting is done -
Razor blades are set into wood blocks. There is soft rubber usually surrounding the blades. Here, the blades sit inside and a little under the green rubber strips.
The blocks are pressed onto the balsa. The rubber recedes and exposes the blades. The blades press hard and cut into the balsa.
In 1970 - 1990s die cutting, there can be slight differences between like pieces on the sheet. This depended on how the blades were set into the wood block.
For fin uniformity, this is why why you should "gang sand" the old style die-cut balsa.
Stack, hold tightly and even up the fin edges.
On the right side picture, I've sanded all the sides except the small top edge. You can see it is off before sanding.
After freeing the pieces from the sheet, the edges weren't perfectly square.