It looks like Titian resolved the issue - Together etc in the UK, and Julian and John in the USA (and apparently in Oz too). I wonder whether they thought that the popularity of the "Round the Horne" re-runs at the time would confuse the public about the nature of the record in the UK?
(I notice that it's all 'Together' now also on US Amazon and Oz HMV

)
The Archiv discs I was referring to was
this set (4713172). The main work is actually L'estro armonico Op 3 - single instrument per part but actually sounding quite beefy on discs 3&4. The only 'plucking' is the Double Mandolin on the first disc, which is also available separately under the title "Alla Rustica" -
Galleria 4578972 - but may be being deleted as it's not listed at MDT, but is at Amazon and Crotchet. It also seems to be on an interesting Panorama twofer - 4692202 - which seems to be Vivaldi's 'best bits' out of the 5CD set + the '4 seasons' and the Gloria
here - although note that a new recording of the 4 seasons has just come out which is supposed to knock all others for six (from Alessandrini) - although I've not yet heard it myself.