Following this thread with interest, but from a practical point of view, re: the collar of bandoleers/'apostles' side of things, rather than the Dutch aspect of it!!
As a re-enactor of 20 plus years, who's used the collar and 'apostles', ( really frustrates me that term - see the ECSWA article that has been mentioned!) on a practical basis, there's various ways ammunition and powder was used. Initially, powder WAS kept loosely in the 'bottles', each bottle holding one charge, or shot's worth of powder. The tops of the bottles could be wooden or lead - one of the more frequent metal-detecting finds from ECW battle fields are the lead caps of the bottles. The powder flask held slightly finer ground powder - finer so that it didn't clog up the touchhole and pan of the musket. It would be fascinating to know if this was ACTUALLY the case, given the vagaries of supply, but at least this was the theory.
Even today, different issues of powder can vary wildly, with some being greasy, some fine, affected by humidity or storage etc, and this all affects the firing, and more importantly, the 'running' of the musket.
It may have been the case, that when infantry were firing by rank, 12 shots would have actually lasted quite some time. Units were often 4-6 ranks deep, firing by rank, and going through steady firing processes. With Infantry being deployed in lines, often 2-3 battalions deep, it may have been the case that they needed replenishing less than we think.
The shift to cartridges is something I'm curious about - I've read somewhere that they were in use by the mid-17thc., but not sure where. Certainly belly boxes were issued to troops by the end of the ECW (1642-51), and these surely held cartridges. So maybe cartridges were issued eventually to troops of the late 17thc, when the shift to flintlocks AND different firing techniques became more widespread, enough to warrant the eventual decline of the collar of bandoleers. Wasn't there a gradual shift to platoon firing, and 3-rank techniques in infantry? This would speed up the rate of firing, and thus need more powder. Eventually therefore the collar of bottles/bandoleers would serve less of a function, but powder flasks still be needed for a while?
Interestingly, we've always thought that grass, sisal, cloth or tow would be used as wadding, and would be easy to get hold of, though not sure about the long-term battle-field use of this.
Hope this adds more to the discussion - firing a matchlock musket is a very rewarding experience - and its fascinating looking at it's practical use in history, as well as having 'hands on' knowledge!