RE US notes:
(1) Correct: a "star note" is indeed a replacement note (since 1910),
exactly like a Canadian asterisk note.
(2) Yes, there are quite a few American collectors of very low serials, "solid" serials," and "radar notes" (which have exactly the same definition as Canadian radars except they are 8 digits instead of 7). However, the concepts of "shoulders," "rotators," "repeaters" etc. have not yet caught on down here.
Hope this helps you. Bernard Schaaf