"I missed the deadlines for the NUA treatment"
What do you mean by this? The only way to have "missed the deadline for NUA treatment" is to have failed to meet the requirements for this to be a lump-sum distribution. If the plan did not report on the Form 1099-R anything in box 6, that would imply that the distribution did not meet the requirements of a lump-sum distribution.
If the distribution does not qualify as a lump-sum distribution or you choose to not to treat the distribution as a distribution of NUA, the distribution must be reported as an ordinary distribution from the 401(k) and your basis in the shares will be short-term basis equal to the value of the shares on the date of the distribution. The brokerage should have reported this a a distribution of short-term noncovered shares and generally would leave box 1e blank rather than putting a zero in box 1e. When entering this Form 1099-B into TurboTax, indicate that that the amount in box 1e is incorrect of blank and TurboTax will ask you to enter the actual cost basis.
