The rotor was replaced a few years ago, because it was floating.
Ah! That'd be a good reason to expect the twin timing marks on the other side.
That's like saying "There was no life on the moon, therefore it must be on Mars."
And what if the rotor is off a Royal Enfield? It won't have marks for triples or twins.... on either side. And who is going to guarantee that the marks, if any, are in the correct position?
You guys are killing me. Assuming there are correctly placed strobe marks on the other side is a leap of faith requiring an astounding imagination.
You're also asking the OP to violate the first rule: If it ain't broke, then don't fix it.