Do i need to segregate eligibility per BU when implementing global absence management?

Summary:

We have implemented US portion of the absence management. We have not separated it by business unit or legal entity (used regular person type, assignment status, assignment category & bargaining unit value).

Content (required):

The question I have is do I need to go back and add US business unit to all plans we have implemented so far? Seems like plans & types are based on LDG / legislation while EPs are global. I was able to enroll US employee in UK based plan even if the EP is the same for both, which makes me think the application automatically segregates US vs. global based on LDG / legislation and there is no need to add additional criteria on the EP to ensure they are separated (was thinking about adding business unit criteria but