If you follow their blogs etc. the fact that they didn't have an option for an upgrade to Collector's, or a discounted price if you already have purchased the game, is contrary to what they preach. Their business model is about their fan base and to not have any option for those who 'supported' the game while it was being created is disheartening/disappointing.
I understand too that there had been an announcement about an upgrade for Early Access Steam Accounts but announcing it and actually do it. Are two separate things. (Color me impressed once they have implemented it)
OK stop, Larian are a small independent developer composed of a few dozen guys so it takes time to get everything lined up and ready for launch....they don't have a PR army and hundreds of people. Have patience, there's still weeks to go before release and that's really the only time being unable to upgrade would have any meaningful impact on you.
Honestly, when a developer comes out and says they have a limited number of copies available to the public (1500 in this case) it really makes sense to have all the details available at the same time (like the digital CE pricing and contents). Because while people are waiting for information on the latter to make a decision, quantity on the former is draining away. That's going to stress some gamers out.
This is one of the things I'm talking about when I stated that I wished the selling of the game had been handled better. I know, I know.. how dare I be offensive with those opinions and all that.