I have literally seen burned conductors pulled from underground ductbanks resulting from Neher McGrath calculations not being performed.
Keep in mind, most of the ductbanks I work with don't fit into the standard detail arrangements provided for in Annex B, but similar application. The Engineering calculation effectively are the same as you would come up with in Annex B for standard configurations.
The medium voltage equivalent of Annex B is found in Section 311.60 (2020 NEC) is enforceable. Annex B is not, because it is an Annex.