Of course I have NEVER worked on a project where the models were accepted because model calculated cost was NEVER the number management wanted to hear. All of those projects ran over the officially accepted estimate by 2-3X.
Sometimes management does this on purpose. Many projects don't get serious until they are 1/3 of the way into the project. This leads to shortened schedules in order to force activity earlier. Sometimes management does this because their even more senior management just won't accept the right answer but will pay for cost overruns once they are afraid of losing the sunk cost work already