Thank you codah, and sorry for the misunderstanding.
My original problem was this one : (not allowed to post URLS but check post "Question about using a single event sheet on different level" - last replied wed 27th august 2014 at 6:26 pm)
What I meant with the number of instances is the following : if I have instances 0, 1 and 2 on layout 1, and I'm currently on layout 2, where there is 3 additional instances of the same object type, will they be numbered 0, 1 and 2 - or - 3, 4 and 5 (IID)
And so instances awaing for me on layout 3 will be IID 6, 7 and 8?
While you are on layout 2, there are only 3 instances existing, numbered 0, 1 and 2. When you go back to layout 1, there will still be only 3 instances, 0, 1 and 2. Etc for layout 3. You can check this with Debug mode.