Maps dropping unid'd using Cartography Scarab of Corruption do not always have 8 modifiers

I am running vaal temples (back to basics atlas node + twist of fate) with Cartography Scarab of Corruption which states "non-unique maps in area are corrupted with 8 modifiers". Many maps are dropping unid'd are almost always NOT 8 modifiers. It seems too be a 50/50 split. I thought maybe unid counted as modifier, but when I ID them they only have 4-5 mods which doesn't add up.


It might have something to do with the vaal vessels (most of the unid'd maps are coming from the vessels), but I haven't been able to confirm that. The vessels seem to respect all aspects of strongboxes (which are supposed to drop 8 mods using this scarab) so I don't see why vessels wouldn't respect it.