There are atleast 10 different types of Cocci so just because they've been exposed to one or some there's always the risk until they are older. That's one of the many reasons that it's recommended that you not wear shoes on your place from other grounds.
There's a ton of literature out there..go take a gander.
It's really been an eye opener for me and find being safe is better because it's really easy to prevent. I had some in the beginning with no issues but a couple different batches I wasn't so lucky. .that's all.
I mentioned that in a previous post, but thank you for reiterating. After an exposure on your own property, it can be assumed the chicks have had a chance to build up an immunity, and my own experience as well as Leahs Mom's kind of indicates that. Just because birds are outside on your property without seeing coccidiosis, though, doesn't mean that on someone else's property they will be immune.
None of this means anything to someone not following basic biosecurity measures, as you mentioned. If you're wearing the same clothes and shoes around your birds after visiting another farm, a show, a swap meet, even the feed store, then all of your efforts in trying to keep your birds healthy might as well be washed down the drain! Not only are you risking cocci contamination, but many, many other ugly things that aren't as simple as coccidiosis to fix.
I also wanted to note that the 'exposure' stuff I recommend for coccidiosis does not apply to most other diseases, especially respiratory ones! The vast majority of respiratory diseases in chickens leave them as asymptomatic carriers of the disease--and they will spread it! You do not want your birds exposed to respiratory disease!
(And one last note--technically, coccidiosis is a parasite infection, not a disease, but I'm sure y'all know what I mean in my last paragraph.)
I need to get more sleep before typing out posts--this has literally taken me an hour just to type with how slow my brain is processing right now.
