My proposal is fix the bug!!
The quest is CLEARLY worded in a way that GB donations should be allowed. In addition GE rewards of troops count towards quest completion. It is pretty straight forward. This is a BUG that needs to be fixed.
Why do you think this is a bug? I'm not saying goods from the GB's shouldn't count. I think maybe they should but I don't think it's a bug nor do I think it's clearly worded to make one think GB productions would count. I can't recall myself a quest using goods from the GB's to fulfill the requirement but regardless the wording is "donate 900 goods from your current era to the guild treasury" and if you ask me the key word there is
donate;
Goods from GB's are productions not donations.
Units you gain from guild expedition
do satisfy quest requirements as you say which is weird to me because they use the word "recruit" which to me means you actually have to make them in a military building not win them.
Now, why doesn't Promethium or Oricalcum count towards quests that require "
Gather x goods"? Why is it considered "gathering" from a goods building or GB or Trade but not "gathering" when collecting from the Arctic Harbor or Oceanic Terminal?
Maybe because they are not "goods" but
special goods;