I've had a couple situations (a few years ago) of Y to J upgrade with miles then op-up at gate.

Also some years ago, was twice op-up'd J to Y on an award ticket

Once also double-upgraded with miles on board from Y to F (tried to upgrade to J but it was full)

More recently, I received an op up paid J to F. I had upgraded my wife from Y to J using miles a few days prior, but the gate staff wouldn't either op up her or let me upgrade her once more with miles. (had to decline the op up)

I suspect that the rules (and the IT to enforce them) are stricter now.