When do you change top level assembly revision?

Hello and good day to all.

I guess this issue was discussed many times, but I really need your advice:

Our product has 2 levels - PCB assemblies on level 2 and electro-mechanical assembly on level 1.
Today we are moving up revision for level 1 every time there is a change in any item revision in level 2. The change in level 2 can be a change in the PCB assembly or even when there is a change in the work instructions document. When we have a change in level 1 item the revision is of course moving up.
Although this method causing a lot of revision changes it's OK.

My question is what do you do or suggest to do if I have a future change and I need to make another change for the current production? How do I manage the revisions?
Let me explain: I made a change in the printed logo on the cover that is in level 1 and moved the revision from 8 to 9. The new covers aren't yet in stock so we can still produce under revision 8.
But now I need to make an urgent change in a level 2 item that needs to be implemented immediately for all revisions (8 & new 9)
I can't change revision 8 to 9. Do I open a new revision 8.1 for revision 8 and un-released revision 9 or move to revision 10?

Thank you for all your help and advices.