I suspect Tezca is something of a special case, seeing as he is seemingly a god with active duties and a servant at the same time. It may be that Tezca, or an aspect of Tezca, is always present in Mictlanpa, while simultaneously he exists in LB7 as Daybit's servant. This might also be the case for the handful of actual, non-pseudo divine spirits at Chaldea (i.e. Euryale and Stheno, Quetz).
Alternatively, Tezca's power over time lets him pull off shenanigans like this.
Alternatively alternatively, don't think too hard about it![]()