
Lanathar |

No they haven’t not formally
The high level advise is find a similar monster of a similar level and use their defensive and offensive bonuses and the reskin - adding unique abilities as required - perhaps by using other stat blocks as ideas
For example a yeth hound would be a hell hound with the fire breath weapon replaced by bay (using the owlear ability as a base point). You can remove some HP and add some resistances and also give it fly in exchange for probably reducing something else
It is also worth checking what sort of abilities playtest versions that didn’t make it had and then bumping them up to align with similar level monsters
The same idea applies to NPCs it seems. If you look at say a third level “unique” humanoid enemy they will have very similar attack, HP, ac and saves to the average of the level (I am going off the first named unique villain of Fall of Plaguestone)