Especially with a history of receiving chicks with Coccidiosis from a certain source. The Corrid or Amprolium basically works by starving out the organisms by making (I think) a B vitamin unavailable to them. If you run a course of the liquid medication, or feed medicated feed (it’s an either or choice from what I understand) it should eliminate the problem before it happens, kind of like a vaccine (it is safe to use that word here right? Don’t ask… local Facebook forum again…) after a full course of treatment I believe it is recommended to provide a vitamin supplement as well.It will not hurt them and I would do it. They are undergoing a lot of stress and making sure there is nothing going on is worthwhile in my opinion. It almost always too late to save chicks once you notice something is wrong.
I do think @ILoveDaffy was able to save theirs earlier this year but it is very touch and go. I would treat when they arrived and provide medicated feed. It's just too easy to lose them.
Now I'm sure that someone will disagree with me and that's OK. I don't normally recommend treating without testing but in this case I believe the good outweighs any long term effect.