I've tested this with several packs and different players now. I uploaded a room with base game and Peacemakers Spindl Dining room. To me, and to everyone else viewing - it shows as not using any pack specific items. Having folks test it who specifically did not have Peacemaker's kit, it does not show as missing items in the gallery.
When they place the room - then they get a notice that the items are missing and some have been replaced. Images attached. The room is still on the gallery for verification.
Edit By crinrict: Removed some thread tags. Please ONLY put tags for platforms you have tested this on. Since Playstation/Xbox aren't updated and don't have the gallery atm, they won't have the issue at this point. Also only choose either Never or mods removed as they contradict each other.