Timerover, Marc has explicitly stated in print that there was no OTU at release; there was very little movement that direction in 1977 - three RP games had explicit settings: Empire of the Petal Throne (1976, TSR), Metamorphosis Alpha (1975, TSR), and En Garde (1975, GDW - Frank Chadwick, to be specific - but it also was a historical game, and can be argued as not an RPG, either.)
And, while the 1976 supplements to OE D&D had names that would later become labels for specific settings, the 1976 incarnations had no such role; the adventures were exemplars, not tied to a canon-concept, and the rules were literally just swap in replacements for the less polished rules in the boxed set.
Given that one of the 3 explicit setting RPGs was by GDW, and that Marc knew about settings as game elements, him having stated that the OTU didn't exist should be good enough.
Loren's comments in the introduction to Journal #1 also makes it fairly clear that they were building into a new shared setting. (JTAS #1, pp 2-3.) Note also that the issue is dated 183-1105; this corresponds to the press date being day 183 of 1979.
The first evidence of the OTU as a cohesive setting is in JTAS #2 - which is dated 274-1105, and was printed near day 274 of 1979.
Note that Annic Nova was in JTAS #1...
It's not a good OTU adventure. It is a great example of how to rework the rules into something else whilst still keeping the rules relatively intact. Likewise, in JTAS 2, Loren shows how to build a CT Laser Pistol from the Pistol and Laser Carbine table entries.
Note that the Imperium game was released in '77 as well, and per Marc, the counter mix was in fact built from Traveller, adding several elements which would later become canon - but are called out as not in Traveller in Marc's Imperium Designer's Notes. (Dragon, issue 20, p 4)
Looking back, it's way too easy to project a grand vision having existed... but it's clear from the designer's notes in JTAS and in Dragon that the vision grew out of fan demand, not because Marc had a strict setting in mind. Imperium really is Marc's reaction to Star Wars, and what he saw missing from that movie.