Pretty much as the title says; if I add homebrew spells to the "Additional Specific Spells" section of a sub-class, then these do not appear for characters using that sub-class unless all of those spells are also added to the homebrew collection.

This behaviour seems to differ from spells that are added under the Spells section of a class feature, where it doesn't seem to matter if the spells are in the homebrew collection or not; once the player has added the sub-class they get the spells and that's it. That is the same behaviour as homebrew spells added to a magic item (you only need to put the magic item in the homebrew collection, the spell doesn't matter).

It seems strange for Additional Specific Spells to function differently in this way, especially when it's a much easier way to add the spells for some classes such as Druid. While I'm aware that some classes use this field differently (spells are only added to the available spell list, they aren't always prepared) but I would say that in both cases the homebrew spells should always appear as long as Homebrew Content is enabled – it shouldn't matter if they're in a homebrew collection or not.

The spells aren’t sposta appear at all unless they are specifically in the player’s collection, that’s why we can’t publish subclasses, etc. that have unpublished homebrew spells attached. When they added the “Additional Spell List” subsection to the class feature form they had to do some funky business on the backend to make it work, and it has a whole in it that allows those spells through no matter what.

Quote from IamSposta >>

The spells aren’t sposta appear at all unless they are specifically in the player’s collection, that’s why we can’t publish subclasses, etc. that have unpublished homebrew spells attached. When they added the “Additional Spell List” subsection to the class feature form they had to do some funky business on the backend to make it work, and it has a whole in it that allows those spells through no matter what.

Actually it's not the Additional Spell List section, just the normal Spells section is enough to add the homebrew spells onto the sheet without adding them to the homebrew collection; this seems to work for everything with a spells section (sub-classes, feats and magic items). But the Additional Specific Spells section doesn't match that behaviour, it requires everything specified there to be in the homebrew collection, even if they're always prepared spells.

I know we can't publish such an item without first publishing the spells it's dependent upon, but it shouldn't be necessary for someone wanting to use the sub-class to also have to go through adding all of the spells as well; simply adding the sub-class and selecting it should be enough for the spells to appear as well. A DM should only need to add the spells if they want them to also be available for general use (assuming they're not specific to that sub-class).

To use an example, I've ported the Grim Hollow "Circle of Blood" Druid sub-class for private use, and it has a spell list of eight spells, six of which are "sangromancy" spells also introduced in the same book. I had them all added to the Additional Specific Spells section and it seemed to work fine because when I first tested it everything was in my collection, but since then I pared my homebrew collection right back down, and today I was trying to create a character using that circle and only the two non-Grim Hollow spells appeared on the sheet.

I've since removed all of the spells from the Additional Specific Spells section and instead moved them into the Spells section (laboriously adding each one, setting it to the correct level, setting the "consumes slot", "counts as known" and "always prepared" options etc.). This works as expected (only need the sub-class in homebrew collection, and only when choosing a sub-class).

But that's a huge pain in the ass compared to just being able to add them to Additional Specific Spells, and I may now have to go back through my homebrew to be sure I haven't got the same problem on other sub-classes.