HRE "The Shadow Kingdom" necessarily happens in 1490 if there are provinces in Italy out of the HRE?

[Piccolis]

I'm playing has Austria and the year is 1490. I just won a war against the Papal States and conquered Rome and Umbria. Those two where the last provinces out of the empire. I am then making them cores when "The Shadow Event" happens in May 1490.
I'm questioning myself if this event necessarily happens in 1490 or if it could happen after in this context. If it could, I would reload and try again and with some luck the event would not trigger before Rome and Umbria are my cores.

 

[grotaclas]

The event doesn't need to happen in 1490. It has a MTTH of 12 months. But it usually happens quite fast, because it can happen for any of the italian HRE members.
But you don't need to make the italian provinces your cores to add them to the HRE. They just need to be owned by you or your vassals and then you can enact the decision to rein in northern italy. That adds the provinces to the HRE even if they aren't your cores.