Look, I'm a lawyer and historian by occupation, and heraldry is my hoby. As in most european states of that time, Croatian flag and COA was not regulated by Law until 1868 (and two color flag we were discussing before). But this doesnt means that it didn't have its official design and use. Again, you can read all about this in Jareb's book where you can also see the official Gazette cover pages (where can you see the Triune COA with unidentified crown), published by Croatian Parliament, and also the seal of Croatian Parliament (here is the link to Croatian Parliament site with the depiction of  seal ) I think it can't get more official than this. The alternate version I proposed above was on official flag of Croatian ban. Ro0103