Are you referring to the IBM Systems Science claims (likely apocryphal) in the Pressman paper, or Barry Boehm's figure in "Software Engineering" 1976 paper which did include some IBM sourcing (literally drawn on) but was primarily based on survey data from within TRW?

It baffles me that anyone would continue to promulgate the Pressman numbers (which claim ~exponential growth in cost) based on... it's not entirely clear what data, as opposed to Boehm's paper which only claims a linear relative cost increase, but is far more credible.

Pressman i.e. https://www.theregister.com/2021/07/22/bugs_expense_bs/

In a waterfall, single-deliverable model it wouldn't surprise me there is some increase in costs the later a bug is discovered, but if you're in that world you have more obvious problems to tackle.

People still use the Pressman numbers. So much for "data-driven decision making"...