I got around 1000 notes coming from a web service call every night. I check the nodes for changes and if there is some they will overrule some old data. But now we have all the nodes in a big list and this make it hard to find a specific node how can I sort all these notes in some kind of category.

Sure I could make a list of categories and then put each node in one of them but one node should be able to be in more than one category so then I would have to copy the node to all the categories I want the node in but this will force me to find the same node in more than one category if I want to make some changes to the node.

I think this can be a little abstract so hope you understand my question.
This is how I would like the tree to be.

Category 1
-  Item 1
-  Item 2
Category 2
-  Item 1
-  Category 3
   -   Item 1
   -   Item 3

And then when I change Item 1 it changes all the places where item one is located.
A category can have a sub category.

We have this setup now

ItemList
-  Item 1
-  Item 2
-  Item 3

And then we got the category strucktor in a diffend place like

Category 1
Category 2
-  Category 3

And then on the items we select the categories with a content picker. This works for the fronted but make i very hard to find a note in backend. is there some way I can manage this in a better way so when a note is saved with categories selected then the item will be showed in the categories like in the first example.