Why do some famous TV chefs have almost identical recipes?

I´ve seen sometimes that two famous chefs, whose recipes are printed on websites, will have almost an identical recipe. (When they both work for the same channel, could it be that someone else writes the recipe up for them, and decide to use it on two television shows I wonder??)
Sometimes the recipes are just plain almost identical, and other times, you can tell that the person halved or quartered the recipe, then changed the quantity of salt from a pinch to a smidgen. (I can tell, because I often halve or quarter recipes when I want to test them)
When can you say that a recipe is original and how close does it have to get before you have to say that it is an adapted recipe, or that a recipe belongs to someone else?