If it's anything like the patching in some common bluetooth controllers, the patching area was filled up a long time ago with new features and they don't want to respin the base silicon.

Yeah, looks like it :(

I read out the patch data from two LPC55S69 I have at hand, and...

MCU Date Code: 2019-07-20: 11/16 slots used 2019-11-05: 14/16 slots used