The definition of the conformally rescaled Ricci tensor Rt[li,lj] has
the comment "(* Adding Z term by changing Xtn to Xt *)". However, all
the Xtn terms in the definition are still there. Does this mean that
there is an omission in this expression?

According to Dana, who wrote that comment:

I think that the comment just wants to point out the fact that in CCZ4 the Xt contains a Z inside. So the expression looks the same as for BSSN, but it is not, because Xt and Xtn are no longer the same.

Barry