Correct name of a primary hybrid

[RosieC]

However, wouldn't "veitchiana x equestris" be veitchianna (either the man-made or wild version) crossed back with equestris?

Surely this is...
(equestris x schilleriana) x equestris.

Usually an x between two names indicates they have been crossed rather than a natural hybrid (just as I have written them in fact).

Veitchiana x equestris is not a registered hybrid so would be listed that way rather than as a grex name.

Having said all that I agree with everything that has been said about how wild/cultivated hybrid naming works... I just think this looks more like a back cross of Veitchiana (or x veitchiana) to equestris which is something different again.