The pearl shop currently shows all of the wagon skins being pulled by four horses. The wagon claim ticket sold with the skin is for a wagon supporting two horses. I'm sure the intent was to display the skin in all its glory with a full set of horses, but it feels very misleading when neither the skin description nor the wagon claim ticket specify a number of horses supported by the wagon set being purchased. A player should do external research on the ticket, but I don't think that's a very good argument, when the 3d model clearly shows four horses when selecting the set, and it's literally called a set which suggests what's shown is what you get.

I knew this, and bought a set to train horses with while I get a workshop sorted out, but it honestly feels like a liability because the information is entirely missing in-game before being purchased and registered with a stable.

I get what you're saying, but the wagon skins specifically state the types of wagons that it can go on:

Farm/Trade/Merchant/Noble/Forest Path

The included wagon registration (Farm wagon) is a Bonus, aka they threw it in there "free" (if you want to call it that).  What I would argue for is for them to update the text of the Farm Wagon Registration to state how many horses it uses.  That's the part that shouldn't be a guessing game.