Mutable, child COs can only be used by one parent?

Unreal 5.7.

I’m fairly new to Mutable. I was trying to reuse a CO for some boots I intend to use with multiple parent COs. I used the Attached to External Object property for this with success for one parent CO. However, it’s constrained to a single entry and so I don’t know how I can use it for multiple parent COs. Can someone advise on how to do this?