Going a little off topic but to finish this thought: When you place a note on the items in your purchased list, you will see the note in any store you are looking at and you can also "deselect" the "purchased" wanted list from the displayed items. For example, I am currently completing 20 sets at once and I have about 12 wanted lists for them, 10 for one set each, 1 for general items and 1 for 10 small sets. For the group of 10, I list the set number in the note and after I purchase an item, I add the order number beside it and then move it to my general purchased list (I also have an extra wanted list for one particular set because I need 30 pieces). When I look for pieces, I remove the purchased lists from my searches; both in stores and in items by shop. I haven't ordered a duplicate item yet.
If I have the same piece missing from multiple sets, I list it in each wanted list and compile them into one list when I buy them.
Mods can probably move this stretch to the BL discussion.