I only put a random number in the HOME tracker because PKHeX was showing a message that it needed a value there, so I just filled it in so the alert would go away. I wasn’t trying to guess any correct number. Also, I checked the encounter database, but Ursaluna (non-Bloodmoon) doesn’t show up there either, so I couldn’t use it like you suggested.
I’m only planning to use my Ursaluna for myself, just playing casually in my game. I’m not planning to trade online or battle online, so I don’t think anyone will really be checking my Ursaluna and saying “hmm, this looks suspicious”.