OK, you can breathe now. Fifteen minutes after I sent my query, this reply was sent back to me, and I didn't notice for yet another fifteen minutes.
Yes, the order is a bit eccentric! There's a variety of reasons, more or less sensible. For starters, we began by publishing the last volume of the series (in paperback), because it was the first one we got publishing rights to (the other volumes were then in print with another publisher). As volumes went out of print with the other company and we acquired the rights, we started doing additional volumes, such as Hitler vs Me, but not in the series order. The e-book situation is a little different, because we used more than one method of typesetting the print volumes, and some of the volumes were more amenable than others to conversion to e-book format. We were also testing to see if there was enough of a market for the e-books to justify the conversion process.
I expect us to eventually have them all available as e-books, but because we're a small company it may take a little while. We're actually planning to go back to the beginning (way back) and publish an e-book of the original 1962 version of Three Cheers for Me this coming fall. That was the version that won the Leacock medal, but it is very rare these days, since the revised edition from 1973 was printed in far greater numbers. The revisions were mostly done to help lead the book into a series, the original being a stand-alone novel. I think fans will find it interesting to read the original.