After transcribing a few letters, I wanted to take a look at all of the stamps together. It turns out, I only have four unique stamps across the batch.

6 cents; Air Mail

6 cents; Air Mail

6 cents; Air Mail (imprinted on envelope)

6 cents; Air Mail (imprinted on envelope)

1 1/2 cents; Martha Washington

1 1/2 cents; Martha Washington

3 cents; Roosevelt, White House

3 cents; Roosevelt, White House