Minolta's achromatic coating was a double-layer coating.
Double layer coatings were around since the 1950s...
As for pentax's 7 layer SMC process or Fuji "11 layer" process, in truth many of the "multicoated lenses" may even have single-layer coatings in one or more surfaces. Coating many layers is an expensive process and a manufacturer will choose the minimum needed coatings to get good performance.
In 1971 Canon released their lenses with either a "SC" ("Spectra Coating") process or a "SSC" {Super Spectra Coating) process. The SC lenses were only single or double-layer coated. Canon publicly issued a statement telling that multi-coating is mainly good for increasing light transmission, and that not all lenses or every lens surface will need multi coating. And the Canon 50/1.8 SC lens ranked as one of the best in flare prevention on a 1973 flare test (chart below). It's true that Pentax SMC lenses were the best ranked too, but careful examination of some of them (i.e. 35/3.5) will show that not all surfaces are multicoated.
Table sourced from: Popular Photography 1973