They need authorisation from the developers to assist with certain bugged quests. The same applies for items, though if they can verify you lost but had possession of items they may be able to assist.
If they cannot verify you had the item they cannot. The same if you have not finished a quest, or gotten the item they cannot grant you the item.
Otherwise it is as advised: To create a (forum) bug report to get it investigated.
Current content will be generally in the pipeline for bugfixes, especially content that advances the story or holds back raid content. Other expansions well… It is a case of “is there enough devpower, time and can it be fixed?” There are lots of bugs that will never get fixed sadly enough.