I’ve been playing 40k since the late 80s. I know the lore. I was there for it. I have watched it change over the decades. And sure, the female warriors weren’t explicitly labelled Space Marines, but they clearly were intended to be “the same” as the male models that would become Space Marines. The genestealers in Rogue Trader weren’t labelled tyranids either, but no one claims they weren’t by citing lack of specific lore at the time they were first published
The only reason those models didn’t continue to be made is because misogyny meant the models didn’t sell. So female space marines got written out of the lore, and the sisters, in all ways lesser than space marines, were introduced, so as to not offend the fan base of the time with equality.