Avro Tudor IV models

[The Avgasdinosaur]

Learned contributors,
As I understand it when operated by Air Charter
c/n 1255 G-AGRG was finally classed as a "Super Trader IV"
c/n 1256 G-AGRH was finally classed as a "Super Trader IVB"
c/n 1342 G-AHNI was finally classed as a "Super Freighter IVB"
c/n 1345 G-AHNL was finally classed as a "Super Freighter IVB"
c/n 1346 G-AHNM was finally classed as a "Super Freighter IVB"
c/n 1348 G-AHNO was finally classed as a "Super Freighter IV"
What if any were the differences between these various models of Avro Tudor?
Many thanks for your time and trouble,
Be lucky
David