I have some experience with this so here’s some information. What you have said above is correct about D11 being a family name. All CAT Dozers are in the D Series, D11 being the highest in the lineup.
The different names come from different generations for example when the D11 was first introduced is was named D11N, the new model was D11R and after that D11T. Up and till recently D11T has been the most current version but CAT has now chosen to simplify the naming nomenclature throughout the lineup. Which brings us to the new model the Next-Gen D11 named simply ‘D11’ which the set is based on.
Finally there has been some comments about the D11XE that will be launched soon. This is not a new version but rather an option, that being an electric drive version. Similar to how the Liebherr R9800 has a face shovel and backhoe variant.
Check out this link on the new naming:
https://www.foleyinc.com/new-caterpillar-dozer-nomenclature/
Also note though a D11 is a D11 each one has a spec chosen by the customer which means variations for example part colours, railings, the ladder, blade, ripper, etc…
Anyway that’s my knowledge, hope it helps explain some questions.