Does cooking raw meat/poulty extend its shelf life?
Shelf life for flavor...or for safety?  Two different issues.  Many variables.  How was it handled before freezing?  How was it defrosted?  How is it being stored after defrosting.  Those will all be factors impacting the safety issue. 

Lets say to minimize the safety concerns you roast upon safe defrosting.  Now you have a safe product (from a bacteria standpoint), as long as you handle the chicken appropriately after cooking. Keep it out of the danger zone...even freeze it...it will be safe...but flavor probably begins to degrade over time (picks of fridge flavors...freezer burn if frozen).

Now you take that chicken and make stock.  You pull from fridge (or defrost appropriately) and cook to boiling while making stock.  That kills any bacteria that MIGHT be present (doubtful if you cooked well and handled appropriately after cooking)...so from a safety standpoint you are probably fine.  However, you probably have a stock that is not as flavorful as it could be because of the lengthy holding time.

In the end, I would say (nothing to back this up but my own experience) the final stock has the same shelf life as any stock, but it probably tastes different from one made with the freshest ingredients.