FYI This arrangement, post joining the original and new geometry, which I must confess to not understand fully seems to be deleting the extra vertex just fine whilst retaining the edge split angle.
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The reason that it works is because of the way that blender implicitly converts numbers to boolean values. This should be identical to your solution, but done explicitly.
I hope that help you understand what’s happening more fully.
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Thanks. That’s interesting because I started with a comparison node, but I couldn’t get it to work, wonder where I was going wrong. Maybe I had it still set on float? Unfortunately I didn’t save a file with that so I can’t go back and check now 
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index value 0 is false
index value >0 is true