Four sets were produced to cash in on the television series, but as occasionally happens in these cases, the information supplied to produce the artwork didn't quite match the programme as it was broadcast. You may remember that the Wall's Sausages / Look-In Magazine Star Wars transfers didn't include Han Solo — a similar oversight.
A rather more serious problem was that the artist working on the transfer sheets was clearly basing his figures on tracings from his comics collection. You may be able to recognise panels from Frank Bellamy's Thunderbirds, Don Lawrence's Trigan Empire, etc., etc… it's quite an entertaining game if you're willing to play it. Notoriously, many of the figures for the contemporaneous 'The Black Hole' sets were taken from the comics artwork of Steve Ditko.
Instead of the traditional single background on which to rub down the transfers, these are split into two 'adventures' per set — which may have looked to innocent purchasers as if they were getting a bargain, rather than being short-changed.
(As a side-effect, it's also made it quite hard for us to specify which sets we're talking about!)
Here's how the sets looked from the back while still in their cellophane wrappers:
Picture Credit: SPLAT Scan Archives — StellarX 7 Wonders
© Tom Vinelott 2020