I might trim the excess but I would not remove it. The shirts have been worn & washed with the stabilizer continuing to hold the embroidery in place.

I agree, I would not remove it.

So I can just remove the outside part that is not attached to the shirt? I need to make sure the fusible interfacing attaches to the shirt before piecing and quilting.

I'm thinking you could remove the excess outside the embroidery so the fusible sticks to more of the shirt. When I embroider things, I remove as much of that excess stabilizer as possible anyway.

Jen, whomever did these did not trim closely and that is what concerns me. I think I will sacrifice one of the duplicates and see how that works. Then I will stitch around the embroidery to make sure it doesn't shift.