Thanks for all the replies - most appreciated.
I find restoration quite frustrating and difficult, and the Honda is proving to be trickier than old Brit iron.
Fortunately, the CB 750 is pretty much complete, which helps a lot.
Aside from P & K, I looked at David Silver Spares (DSS), and they don't show the logo part of the seat - why obfuscate?
An email to DSS elicited this response:
Sorry, none of our aftermarket seat covers comes with the "HONDA" logo on.
It is Copyright infringement to have the word "HONDA" on aftermarket products.
When I recovered my Bonneville seat, it was easy to buy a cover with the Triumph logo on it.
There were no problems with the copyright holder, even though it was a non-OEM part.
Again, I bought a complete seat for my Commando from Andover Norton, without Norton complaining or threatening legal action.
It's ironic, hypocritical even, that Honda, a company which copied so much from the British motorcycle industry, should be so litigious.
I emailed P & K with two questions, but they didn't answer one of them.
I had to email again about the free "strap", and the reply revealed that it was missing the buckle.
This wasn't obvious from the website or eBay listing - obfuscation again.
You have to ask all the right questions, otherwise you end up with incomplete components.
I think I'll sit on this problem for the time being, and do some more investigation later.