Leaves and coins can always be completed in the zone you find it in. In the case of Antonica ficus leaves, they can be found in either Antonica or BB.
Shards and bones are progressive quests, meaning you will find the lower level ones first (shattered bones in T1 zones), then in T2 zones you find cracked, and in T3 you find weathered, etc..
You may also notice that certain bones can only be found in certain zones, such as gnoll bones in BB (shattered - weathered) and then unscathed and encahnted in TS.
On top of all of this, some different nodes in zones will or won't have certain things available. There are some for instance in the commonlands which do not have the commonlands leaves, but they have orc bones instead. While others won't have orc bones but will have the commonlands leaves.
Hope that helps.