A list of bonus IDs has been found for all of these sets except the BFA season 2 ones. Happy to assist and offer more details as needed.

It works in the default UI. I am happy to help investigate further. I was actually able to create the plate elite set from Shadowlands season 1 by putting the appearance IDs and modified appearance IDs into SavedVariables. Part of the reason I think it worked is because the regular S1 items didnt show in the catalogue.

Did you try to reproduce the issue by following exactly the instructions outlined in my previous comment?

Hi,

Could you clarify which items you are having issues with? And what is preventing you from previewing them?

Yes @Lombra

The items I am having trouble with are all the Elite PVP transmog set pieces from BFA seasons 1 (Dread Gladiator), 2 (Sinister Gladiator), 3 (Notorious Gladiator), 4 (Corrupted Gladiator), and Shadowlands seasons 1 (Sinful Gladiator), 2 (Unchained Gladiator), 3 (Cosmic Gladiator), and 4 (Eternal Gladiator). For me, none of the elite appearances appear in their respective armor type catalogues except for SL seasons 3 and 4. To fix this, I have manually edited my SavedVariables for MogIt to include all of these appearances. That said, if I right-click these items to open a preview window, the regular gladiator transmog shows instead of the elite. If I try to import any of the elite pieces from WoWHead or by inputting the bonus ID, the same thing happens. I don't know why this happens, but it does.

I understand. If you link one of these items into chat, and then Ctrl-Left click it to preview it in the default UI, does it show the correct item? If not, there probably isn't anything I can do about it. That's an issue that occurs with handful of items. If yes, I would have to investigate further.

Yes

Yes and no. If I link the item directly from MogIt, it does not always work. However, if I have an elite set saved with item pieces not listed in the catalogue, I can still link it in chat and get the correct appearance. Typically though, it doesnt work. However, I have found ways of linking these items using other addons and getting the elite appearances in the dressing room.

@Lombra I have found a solution! All I did was update the bonus ID list in the addon's core. From there, I was able to import essentially anything. If you would like, I could send you what I've done for a future update.

I added my findings as a separate pull request. Happy to help keep the list updated as more IDs are introduced.

Great! Ah, bonus IDs... I had almost forgotten about those.

Would love to see your findings.