I've not yet seen any advertising that links it to the Other Ventures series. It's only that odd manual (linked earlier) that has a single reference, in the loading section, to Other Ventures. Despite that, I think that's a fairly strong case for linking the game to 'Other Ventures' but it does still feel a bit odd because the compilation it supposedly came with does not even list Saigon on the box. It's almost like Saigon was thrown into the compilation last minute (or later on) as a freebie.
If we were to add it to the series, is there a reference anywhere that denotes Saigon as 'Other Ventures #5'?
Because, as I said earlier, Dog Star Adventure was officially Other Ventures #5, as clearly shown on the packaging...

So would Saigon be #6... or might there potentially be other games that slot in earlier? It's obviously a game that was "another venture" for Infocom, but was it actually an 'Other Venture''? If Adventure International had abandoned the use of the series 'Other Ventures' by the time Saigon was released, then did they consider the series to have still been ongoing?
(Edit: for typo)