<That said, I don't think we should be too worried. One of our three weekend letters - Belli - was hand-cancelled on a Saturday, whilst we have the example of the 'Dripping Pen' letter, which was alternatively machine-cancelled on a Saturday. So, even for Saturday, there are clearly both options available - the former, as we are supposing, being the method of processing hand-dropped mail to local destinations. It would at least seem likely, then, that the same would be the case for Sunday, but we'll see, I'm sure.>
My thought is if it is established that the machine cancellers didn't run on Sundays, we can then (hopefully) deduce that the two letters that received the Sunday hand post-marks did not receive them for the reason of being rejected by the machine cancellers.

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