The situation when somebody has designed a Variable Font and it's in-between interpolations are accidentally very similar to other designs is rather unlikely...
But what if somebody does that with my design? (shame on him!)
This is highly connected to font copyrights which as i recall may be different depending on the country?
Anyway, here's a simulation:http://quick.as/DvvJCj7Pe
(i added "True" instance just so it's easy to view the interpolated "accident")