I would deeply appreciate some more detail on the heat study and cleaning fluids RC.
But, how many flocks have Mareks but are asymptomatic? It's uncountable.
An asymptomatic flock is not the same as a Marek's free flock.
Dr Mark was saying wildbirds = Mareks, which means any outdoor flock has it.
The only things I can state with certainty are that one pullet has symptoms, two other pullets have it but are asymptomatic, and the hens most probably have had it for a long time and are asymptomatic.
I think it would be wise to seek a pcr test for one of the hens prior to relaxing quarantine. Maybe Marek's is what Erica and Ivy died of.