So you want to make a page for a horse from an early series (up until Treasures), but you can't figure out what herd the horse is in because it's not on any version of the card or anywhere in canon lore. What do you do?
I advise that you use this list of questions to narrow down which herd your horse is in. However, there are exceptions to these, like Royce (an alicorn who is in Herd Moonfairy but may have been born into Herd Airistos because of his feathered wings and non-spritelike name).
Is the horse a pegasus/alicorn with feathered wings? (If yes, and no to all the other questions: Airistos)
Does the horse have a name that reminds you of the desert/Arabia? (If yes: Shahazar)
Is the horse a hippocampus - does it have a fish tail, or is it an actual seahorse? (If yes: Islandar)
Does the horse have a name that reminds you of winter, snow, and ice - but not the holidays? (If yes: Valeryk)
Is the horse named after a flower or plant? (If yes: Sunflower)
Is the horse named after a constellation, celestial object, deity, or phenomenon? (If yes: Starlight)
Is the horse fairylike with a name you can imagine being mentioned in A Midsummer Night's Dream? (If yes: Moonfairy)
Is the horse named after a Greco-Roman or Norse deity? (If yes: Pantheon)
Does the horse have a name that reminds you of the holidays? (If yes: Elemyn)
Does the horse have a name that reminds you of the Wild West, or is the name of a Native American tribe? (If yes: Mustang)
If the answer to all of these questions is "no," the horse is in Herd Bellasara.
Hope this helps!