Enough similarities and enough differences that a prototype seems the most likely explanation to me. It could be a replica, but a few strange choices if it is.
I had this British Eagle frame powdercoated:
https://www.retrobike.co.uk/threads/1993-british-eagle-exs.443781/post-3239205/
If the powdercoater knows what they are doing none of those should be an issue. Properly masked and applied, no need to face the BB or headtube after, or ream the seat...
A year too new, but my 1993 GT Xizang is still tentatively for sale if that floats your boat.
I'd only really be interested is a sale (or swap for a larger/earlier Xizang!) though.
A couple of relevant posts:
https://www.retrobike.co.uk/threads/show-us-how-you-fixed-crack-on-manitou-fs.379748/page-3#post-3003616
https://www.retrobike.co.uk/threads/7005-head-tubes-cracking.492709/#post-3723211
There may be more.
Is the blue frame still available? If so, I think I know what it is and if so my friend had one I built for them which was then stolen. I'd love to do a project to rebuild it.
If frames are being dropped in Worksop I have friends there who would be happy to keep it in their garage until I next...