Going back to the original Marek's discussion, the vaccinated chcicks should NOT be mixed for their first few weeks with the adult UNVACCINATED BIRDS for the chick's sfety (in not contracting Marek's). Otherwise & later, it is no problem to mix vaccinated with Unvaccinated Marek's.
Your "not to mix rule" just applies to LT or to Fowl Pox also?
Thxs, Chris