I have a similar 'test' going on in my incubator right now. Wasn't really intentional, I just had some open spots in my incubator so I grabbed some eggs from the fridge not really thinking they would develop. Not sure how old they were but probably 2-3 weeks. Just did my first candling and it looks like 4/5 of the fridge eggs are developing just fine...There were quite a few clears in the non-fridge eggs too so the one not developing could easily just not have been fertilized. Gotta have a chat with the rooster...