Dear Boring Games
It's all sorted! Itch.io support have freed up the Steam Key and corrected their records on both this and four of the other titles I have purchased previously purchased on itch.io.
Thanks for your close attention and my apologies once again for bothering you. I very much look forward to enjoying your masterpiece on Steam and, of course, contributing a positive review in support of the cause.
Grateful thanks and very best wishes for the further success of this and future titles.
Falco