Not sure if it was called "beta" or "alpha" and "closed" is of course up to interpretation, but it was indeed by invitation. Swedish law at the time (still?) had a clause about permitting sharing copyrighted material within a limited circle, which I know Spotify engineers referred to as somewhat legitimising it. I also know for a fact that once the invite-only stage ended there was a major purge of content and I lost about half of my playlist content, which was the end of me having music "in the cloud". Still, this is nearly twenty years ago, so my memory could be foggy.