Commentary on James Maliszewski's article The Long Shadow of D&D:
The period of 1977-1979 is interesting. The first Basic Set came out in Summer/Fall 1977, and pointed players to AD&D, yet there were no AD&D books yet available! Due to delays the Monster Manual didn't make it out until just after Christmas in 1977. Furthermore, the Monster Manual shows that AD&D was till very much in development as it contains a number of OD&D-isms: 5-point alignment system (as used in the Basic Set), no AC over 9, spell progressions per OD&D (see entry for Naga), devils have an innate "Raise Dead Fully" (an OD&D spell later replaced by Resurrection) and magic missile requires a to-hit roll (see entry for Yeenoghu). The Monster Manual can be used with OD&D with hardly any changes. So the era of AD&D didn't begin in earnest until mid-78 when the Players' Handbook first arrived. My sense is that most players of OD&D ignored the Basic Set but used the Monster Manual with OD&D, but most began to transition to D&D or other new RPGs when the PHB arrived. TSR also started releasing modules (the Giants and Drow series) in 1978 despite the lack of the DMG. So to play these you still needed to use OD&D.
More discussion of the "five point alignment" era here:
The Lost Edition (thread started by Falconer).