Your bona fides apropos birds are impressive, and not in dispute, I'm sure, but the RSPB knows a thog or two about birds, too, and on its website it refers to robins which come here from Russia etc. as 'immigrants'.
That makes them migrants in my book. There's a slight difference between curlews moving down from the moors to breed, and robins flying here from Russia and Scandanavia.
"Starlings that breed in eastern Europe, where winter is much colder, migrate to the UK in winter. The same goes for chaffinches, robins, lapwings, coots and many other common birds"
Those words are from the RSPB website.
I suggest that we cease dancing on the head of this particular pin - I realise that you know a lot about birds, etc., but I prefer to take the word of the RSPB in this case.