Prevent data model mess ups due to fieldsets (best practice advice?)

By accident, we (I) completely messed up our data model while adding three new field set (on three different entities) and adding fields to it.

The situtation: In our model we had 'general' fields types which are (were) valid for all field sets. In the settings the {fieldset} field remained empty (see pic). Other field types were assigned to one or more datafield sets.

For a new productgroup we had a list of fields which needed to be seen for this specific fieldset. In Control Center I added the new datafield and added the necessary field.

The result is that any of the 'general' fields were afterwards ONLY assigned to the new fieldset !!! For those items which were already assigned to one or more fieldsets, the new fieldset was added and there is no problem.

@INRIVER, I think there should be a safeguard to prevent this from happening for other users, in other words: the system should show a WARNING, that if user proceeds, the field will be ONLY assigned to the current fieldset or preventing this from happening!!

Secondly, we are now in a debate on how to solve this situation, and make it future-proof:
You advice would be helpful on

How to set up the system for now forward, to prevent this from happening again (best practice?)
- set all 'general' fields to available fieldsets ?
- keep the general fields but put them in a different category, which can then be hidden?
- any other ideas?

And a lot of extra work again to set all settings MANUALLY in control centre.