So I started some chicken stock but went out and was gone longer than I planned. The stock reduced to maybe 200ml. Once it cooled it was really gelatinous and smelled pretty good. Can I just treat this as super concentrated and dilute it as needed?
As long as it doesn't taste burned, yeah. Ideally your stock will always be super gelatinous regardless of if it's reduced insanely or not. More chicken wings help on that front, between the wee bones and skin/cartilage.
Basically, if it tastes good, use it.
I made chicken stock yesterday. Usually I reduce it until there's about 500ml left. I used 2 chicken carcasses and 1 hind quarter and I didn't bother to roast anything and flavour was still really good.
It's gelatinous because of the gelatin found within the bones, cartalidge, etc. of the chicken. You don't have to dilute it either if you don't want. Put it on the stove and it will just melt to a liquid again.
good stock SHOULD become a gel when cooled. adding gelatin to sauces is the whole point of using stock.
I hope you haven't been making bad stock your whole life, anon. congratulations on your 200ml of success though