I re-read DHCR Face Sheet #40, and I tend to agree with you. At best, DHCR is ambiguous on this. Maybe intentionally.
But it's certainly not in my best interest for my rent to be raised 80% to the legal regulated rent. So for now, or at least until the DHCR makes this clear, I'm stuck with high rent increases in a 421-a rent stabilized building, in-between preferential and legal regulated rents.