I went through my notes and this was all I turned up for the idea of overlap, though I've a sneaking suspicion that there are a couple more statements out there that are in the more recent books and which I did not copy down. Of course, we also must judge those as coming after the very influential Masefield text. Even the first quote, by the folklorist Gilchrist, might have been a mere reflection of Masefield, whose book had been published, I believe, within a few months before that statement. Gilchrist did not observe overlap; she is just using what she'd heard/read as an explanation for the irregular meter.

If it was a very prominent feature, it is curious that people did not remark on it more.

I have also felt, like Gilchrist, that some overlap was implied in the way singers alone gave their songs to collectors or how people were "forced" to notate them. This isn't direct evidence of overlap, but rather a reasoning that it may have been there since otherwise the meter gets screwed up. I took this approach on an experiment with bringing to life Harlow's "Sun Down Below". If one interprets the song exactly as written (as has been done in the Revival version), we come we an irregular meter. This is not to say that irregular meter could not have existed; it actually sounds plausible and OK to me. But I thought about how the Caribbean shanties (in which this is included) tend to have a choral response that comes in like clockwork, to a regular beat. So I interpreted the rests and barred-notes at the ends of phrases as overlap. It's this sort of overlap -- in perfect time and not giving short shrift to the meter -- that I imagine would have been the case in Gordon's reference above about the boat rowers.