Materials used in Blocks

Hi folks,

Our sailboat model (RH v5)  includes some deck hardware (winches, blocks, etc..).

These are organized in multiple files, and organized in several levels of RH.Blocks.
Now I'm using nXt full-speed ahead, I did specify  a nXt material for each (sub)part (object).

First time, and first assignment of material, I did exported that *.armaterial file in my lib folder.
Later object definitions using same material are made by importing the *.armaterial file and assigned it tho the aimed layer.

Now the issue.

What happened on the upper level,  a model importing several sub-level object(s) and their material definitions (same original file, remember), is that materials are ** sometimes** duplicated with name suffixed by '00'  , '01' , ... etc
But the issue is : why are some materials duplicated, while others RH.layers of imported blocks use the same original material.

Typical deckware levels : Sheave -> Block -> MultiBlock -> Cockpit Area ->SailBoat model.

Questions : 

1. May I delete the '00'  , '01' , ... materials, if they are not used (in layers) ?
2. Why some block imports do make duplicates, while other don't. ?
3. Is there a kind a UID in the .arMaterial file ? How to read it ?
4. While making an update of the imported blocks, and the material in that imported file has been changed, there is no material update or creation in the main model. This is maybe intended.

The best,

William