Yes, the figures from BuiltWith are still very likely to be much lower than the true figure. I’ve no doubt it will be well over 1000 sites but, before you ask, I couldn’t even attempt to guess. It’s just that we all know for certain that the figures they produced last month were waaaay lower than they should be.
Just as an example, it showed only 3 sites in The Netherlands when @klein has over 50 active sites himself.
But at least BW now seems to be able to detect CP sites better than it has in the past.