Thanks Jeff.
Yes, I found that document when I was looking at the CC requirements. I took note of the suggestion to use Interra Baton software to perform QC on the video before submitting it but, even as a long-established IT business, have had no luck in contacting them for a trial version (I guess it may be a Corona issue).
Thanks for highlighting the progressive format issue. I guess the only thing I can do is to submit the movie and see whether it is accepted.
Charles