DELTA - Why is there a discrepancy between social groups and urbanity fields in the quick reference guide?

The advantage of DELTA is that there’s more detail than the 68 PRIZM segments. So, we may have taken a segment from DELTA that is 60% suburban and 40% urban and combined it with a segment that is 70% urban and 30% suburban. In the end it becomes a PRIZM segment that is 60% Urban and 40% Suburban. We can call it Urban for the Social Group at the PRIZM level and identify that the 2 DELTA segments come from different urbanities, hence the discrepancy in the quick reference guide.