The reason why some late imports "qualify" for ULEZ is to do with the entries for the date of registration on the V5. There are "Date of first registration" and "Date of first registration in the UK" entries on the V5. I suspect that if there is no evidence provided for the first, it is entered as the same as the second! The DVLA's logic is such that if it was first registered after a certain date it must be EUx! I have no explanation for Erling's 1.4Tdi! You're probably wrong to blame TfL - it's all down to the good old DVLA.
If you have an 1.2Tdi, for emission purposes they would qualify as EU4 because they meet the latter's emissions standard. I have a letter from a government under secretary to prove it. Not that diesel EU4 is much use in the UK!
RAB