During the chase scene at the end, it is shown on one monitor that the THX budget is 3,410 units over the budget of 14,000 units (24%). A voice had stated earlier that accounts are to be terminated when they exceed their original budget by 5%. When the account/chase is terminated, we hear a voice say that the THX project is 6% over budget, which would be 840 units, not 3,410.
At the end of the car chase, the view from within the car shows it sliding into the scaffolding and the right side of the car hitting first. But the next shot from outside the car shows the car sliding into the scaffolding with the left side of it hitting the scaffolding first.
When THX is shouldered, naked, by the police in prison, we can see his short shorts tan line on his leg - pretty impossible for people in an underground city. (Unless, of course, there are solariums/tanning salons in the city.)