Back in the February-March confusion of letters, it ended up being the postmarks that confirmed the correct order of letters, in addition to some letter content and the style of writing paper. All those things pointed to the handwritten letter dates as incorrect, something that turns out to happen occasionally, but more often in the early letters.
This recent puzzle in April 1942 was not that easy to solve. I even made a chart to compare paper type, letter contents, written and postmarked dates, but nothing stood out as a clear pattern, so I just went with the handwritten dates as gospel. The variation and sequence of postmarks could be due to Ruth putting letters back in the wrong envelopes, letters being delayed at the post office and not postmarked in a correct sequence, or even Walt forgetting to send them in order and not mentioning it.
The real oddball is the envelope with no letter. It’s postmarked April 25, and I’m sure it originally contained a letter, although that would be pretty funny if Walt sent an empty envelope on purpose—he would not be able to resist pointing that out in a subsequent letter, though—Ha! Rather than give it its own page, I’m just going to post it with the letter of the 25th and its envelope.