I generally agree with your bottom line. But in a legal setting that doesn't do much for you because he would say he didn't have first hand knowledge; he was just repeating a remark he had heard from his mother; it isn't really substantive. Which is I suppose why the comment never got great attention.
Further, your view of the transportation issues is in fact excessive. Early on the long thread, copies of the original BOAC schedules for August of 1961 are posted. I had some knowledge from the period because a law school classmate of mine who was several years ahead of me in the practice was involved in a lawsuit in the area and taking depositions there. He was driving to Vancouver BC to take the reverse flights.
There were two or three scheduled flights each week leaving Nairobi and connecting through Glasgow Scotland and Vancouver BC. There was no real impediment to her being on Mercer Island on the third day. Further, there is almost a full additional day in the time lag between Nairobi and the West Coast of North America.
Even if his mother had told him that was the case there is a paper trail, for one there is her passport documents, and there are flight manifests and port of entry records that must be maintained for legal reasons.
Her name and possibly his cannot just disappear from such records.
Ping. Begin at #792 and read to end of page.
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I don’t know if they still do it, but years ago, if a pregnant woman wanted to travel, they couldn’t be in their third trimester. Something to do with pressure, etc. that might cause them to go into labor.