I current have the Aspire, so I obviously can't see SUB offers for a Hilton card upgrade now myself. But I did get SUB offers before for an upgrade from Hilton no-fee to Surpass, and later another SUB offer for an upgrade from Surpass to Aspire.

And after logging in and clicking Credit Cards from the menu and then See All Credit Cards, at the top it's currently showing me SUB offers to upgrade my Gold to Platinum and to upgrade my Everyday to Everyday Preferred (which I already did once a few years ago, and then later downgraded to no-fee Everyday again).

So that proves they can sometimes even repeat SUB offers after a downgrade, even during the "lifetime" period when you couldn't get a SUB again for a from-scratch app unless you were targeted.