Technically you can fulfill any number on your turn, though given the hoarding nature in your group, I would understand a house rule.
For what it's worth I dislike that rule on items. My group tried to rule that items auto-completed when you have the given resources but that obviously has downsides of reducing planning and in my case would have made it impossible for me to build one of my buildings that shared a resource cost with an item I had before the game ended.
I convinced them to interpret items as optional timing of when to use them - as you seem to recommend. But now I'm holding all my items because there is no reason to ever complete them until the last turn of the game. Why jump ahead on the VP track and look more threatening or give up options of ways to redistribute resources differently if emergencies come up? I just put the resources needed for an item on it and set it aside until my last turn and that way I can rearrange and use my larger resource pool as needed.
This seems really annoying but auto-completing items is awful too and house-ruling a once-per-turn rule seems kind of hacky and still doesn't really fix the problem but rather just diminish it to hoarding one item at a time.
I guess I kind of wish there were some kind of opportunity cost for not completing an item when you can. Maybe like only one "consumable" card can be used per turn? Like one Item or Treasure or other one-shot type effect total per turn? The possibility of missing out on the best timing for using an Amulet later would definitely stop my item hoarding behavior in most instances.
This isn't the biggest deal but it is slightly annoying and feels like it could be improved.