Not quite correct, there were female models in power armour released with “rogue trader”, but very little lore and nothing specifically referenced female space marines. When they began actually writing 40K and 40K lore then they introduced the concept of the geneseed and it only working on males and they also introduced the sisters of battle who are indeed females in power armour but are not considered to be “female space marines” as such. None of it was actually retconned, it just wasn’t explicit in “rogue trader” and later became so when the first actual 40K edition was released.