Very nice collection. I was particularly interested in the last cover addressed to an Edson Rogers of Lawrenceville, PA that showed a rather interesting postmark that is hard to read. I finally discovered that it is from Whitney's Point, NY.
Armed with this information, I was then able to pull this biographical sketch of the addressee, Edson Rogers:

Although this has nothing to do with the cover itself, look at the above recited text: I don't recall ever seeing paragraphs of info. like this with the use of only one period at the end of the first paragraph. All of the other sentence endings merely add spacing, no period as a punctuation. In fact, if you look closer at the text, there are no dots at the top of any of the lower case letters such as "i" or "j" either. I wonder if this was an old fashioned way of printing?