Trouble Displaying instruments in C.A.M.P display cases

Hey all, so recently I've undertook a little adventure of mine: to collect all known instruments (as junk items) found in the game, and display them in my camp/crude "museum". Though there's one small problem... I can only display the trumpet in my display cases it seems, and I cannot assign the accordion, acoustic and steel guitars in the display slots, nor do they appear unless I just check my stash box or sell them on my vendor machine

The only item display cases I have are the normal display cases and that Thanksgiving display case. Could this just be a bug or are the items just that big for them to fit-? Are they just not meant to be displayed at all? Also my bad if I seem to be 'textually' freaking out here, I may be starting to become a rare junk items enthusiast.