Core books players vs DM modules

[graphil]

So for Xanathar's Guide as a DM, if I load the main and the players then I get 2 copies of things like Cleric in the Classes section.
However for Tasha's if I load both then I only 1 copy of Cleric in Classes.

Is that just because of the way the modules were build or am I doing something stupid?

[humby]

It's because of the way they were built - in some of the older books they were included in both, but that was stopped a while back because of the duplication you mention and now the classes (and similar data) are only in the players modules.

I seem to remember it being mentioned that they didn't go back and update the previous books because this would cause issues for any characters built using them.

[Zacchaeus]

humby is correct. There were a lot of complaints about duplication of races, classes etc so after Xanathar (I think) all player facing material is only available in the players module. This cuts down duplication and also errors caused by characters being created partly using the DM module and partly using the players one. All the information is in the DM module - just not in a form that can be used to build characters. Also as humby says there isn't going to be a revision of older modules lest that cause issues with characters built using the DM modules.