Congress is considerable source of explicit allowance for overages in such projects, including at times forcing politically popular purchases that military doesn't want. While forcing inefficiencies in procurement from projects having to buy votes by spreading production.
Ah yes... The sordid NASA/pork barrel effect. I am aware. That's orthogonal to the fact that Congress, besides setting the budget is also tasked wit Oversight. I'm damn sure they've not done/doing a great job of it, because there are many members of the legislature who find themselves straight up lied to by the Executive, yet nothing is done in terms of consequences.
Many examples of the IC lying to Congress can be found with digging. Dirt can absolutely be dug up if Congress sees fit to do so. They just haven't seen fit to glex their oversight powers.
