First, I want to say that I really, really like this game. Thanks, dev team! (It seems appropriate for my first post.)
Second: so I’ve beaten everything I can find, but I have 180 stars and there’s still that last bonus level… And the fact that I need 21 more stars hints that I might have missed a few stages. Is this intentional, maybe leaving space for a future update, or should I get some glasses and look again?
Have you played New Game+ mode yet?
I know what the problem is. In my save, I don’t see sidequests in Normal game. That’s 3x7 = 21 missing stars.
Should they be available? (is it just the old, many-versions-touched save being broken? Or did you just forget that SQs are not included in normal?
I thought about it some more, and I think that side quests might not be giving stars in actuality, even though they appear like they do on the map. That makes the math work out. And I started this save completely on the new version, so I don’t think that’s the issue.
Hey there:
Sidequests don’t show up in normal mode, I think that’s intentional. What may not be intentional, however, is Anthony not remembering that and using those extra stars for the bonus unlock requirements 
And if sidequests ARE unlocking in normal mode, I need to take a closer look at what’s going on.
Looks like the sidequests in NG+ isn’t granting their stars. I’ve confirmed this by starting a new NG+ game.
If that’s the case, then I’ll add it to my buglist for the next patch. This is high priority!
And here Lars was trying to blame it on my being unable to count. 
Thanks for spotting this everyone!
Found the bug:
for each(var pd:PearlData in Main.index_data.pearls) {
if(pd != null && pd.type == "battle"){
Changed to:
for each(var pd:PearlData in Main.index_data.pearls) {
if(pd != null && (pd.type == "battle" || pd.type == "sidequest")){
Fix will be in the upcoming version 1.0.2 patch.