I know, I read the documents. I choose multiple because it is for Heroine Anthem 1+2. It may only be two games, and very similar games at that, but that's still more than one.

Pointing it to Heroine Anthem would mean adding the actual Heroine Anthem 1 OR 2 game to the database. The entry could only point to one. It just wouldn't be technically correct. Because the system works on individual games, that's why the multi-game option was added.
I made the descriptions directly from some of the information you had in the docs, therefore the description explicitly mentions HA1+2. I figure that's clear enough.