Anything that contradicts previous canon is a retcon.
It has always happened in Glorantha, since the very early days. If you read some of the early Wyrms Footnotes articles, you see that the names of Deities have been changed and what they do has been changed, even parentage has been changed.
Does it matter? Yes and No. Yes, because people buy into a particular version of events and don't like it when it changes. No, because that is the kind of thing that fires up religious debate in the real world, so could well do the same in Glorantha.
For me, these retcons are the same as a Glorantha Hero going on a HeroQuest and coming back with a new insight into a deity. His followers are going to believe that and follow him, other people won't care or will stick to their previous ways and think of the Hero as a heretic or just plain wrong. In a Polytheistic setting, there is a lot of differences in how a certain Deity is worshipped.
So, just treat them as a different way of looking at the Deities concerned and stick to your preferred way if that's what you like.