I think there may have been a miscommunication somewhere. I finally got my computer back, so I downloaded the latest save to see how things have changed and... there's exactly 1 display in the Museum. It's the backpack I left there in the original save file. So I poked around to see where the submissions went... seems a lot of the animals were butchered and turned into bone goods. We have carp bone scepters, crundle bone crowns and albatross bone figurines, all patiently waiting to be sold to the next merchants to come along...
So I'm thinking, that maybe there's been a miscommunication here:
The whole point of this game is Have one of every type of thing in the world ON DISPLAY. I really can't stress this enough, guys: the items submitted for display in the Museum, that gives Players the right to play in the Fortress mode is that their submissions are PUT ON DISPLAY using the handy "Display Pedestal" workshop or by being put in a room with windows and forbidden from being turned into crundle bone scepters or eaten by hungry dwarves.
Maybe some Players aren't used to Fortress Mode, though, and are distracted enough by Life to remember that if something is sold to merchants, that it's not at the museum anymore and will therefore never be put on display.
Anyway, so I figured I'll be CRYSTAL CLEAR now: If you begin your turn for Fortress Mode by reclaiming the Museum, before you unpause the game or do anything else: go to the pile at the bottom of the submission chute and forbid all of those items from being used. Carp bone crowns or peahen bone bolts are not skeletons of carps or peahens - they're crowns and bolts. The reason the submission chute is so far away from the Museum is because when you actually decide to put the submissions on display, they're at the VERY END of the list, so you don't have to go searching for them. Of course, that only works if they stay there!
I've prepared a step by step guide to constructing a Display Pedestal just in case this is where the communication interrupt has happened:
Step 1: Start fortress mode
Step 2: Reclaim the latest Museum
Step 3: IMMEDIATELY go to the bottom of the submission chute and forbid all of the submissions there
Step 4: Either unpause the game and build a special place for the submissions or go directly to step 5.
Step 5: Pause the game (if not already paused).
Step 6: Go to the forbidden submissions pile and unforbid the item you wish to put on display.
Step 7: Press "b"uild, then "w"orkshop.
Step 8: The "Display Pedestal" workshop has no letter associated with it, but it's at the very bottom of the list, so press "-" to highlight it then select it with "Enter".
Step 9: Place the "x" where you want the Display Pedestal to be built and press "enter"
Step 10: Select which type of block you want to make the pedestal out of (we have many basalt blocks available right now)
Now you'll be presented with a short list of everything in the fortress except the stuff in barrels or bins.
Step 11: Press "x" to "e'x'pand the list to individual things, instead of the general types of things
Step 12: Press "-" to go immediately to the end of the list. Your chosen item from the submission pile will be waiting for you there.
Step 13: Highlight the item and press "enter"
There! That is how to build a Display Pedestal with a specific submission in it! Repeat this process from Step 5 until all original submissions are placed on Display Pedestals somewhere in the Museum. However, it's important enough to repeat yet another time: If it's not put on display it doesn't count!
I need to also mention something else: even though it states it in the OP, maybe it was too buried in easily skimmed text so I'll repeat it here: Players MAY NOT deconstruct any furniture, buildings, or workshops that were built before, they may only add new furniture, buildings, workshops or excavations. The save file I downloaded has several floor tiles and a wall removed in the Museum, so this has obviously not been understood by at least one Player as not allowed.
To help others to find the important bits when skimming through the OP, I've highlighted them in orange. I'll probably also put a copy of the Display Pedestal step-by-step guide in there too, for easy reference.
When wondering what category something is that when you're deciding what goes onto a Display Pedestal, the last word in an item description will tell you: A donkey bone crown is a "crown (bone)". A mangled donkey skull is a "skull (donkey)", a carp skeleton is a "skeleton (carp)". In this way, we will know specifically what's on display and what isn't. Since we now know precisely what is on display as of ptb_ptb's turn, we can mark off "leather backpack" in the list.