I reiterate the point made above: In oligopolies, we use a concept of game theory called Nash Equilibrium. If a game (in this case and oligopoly) is in Nash Eq., this means no firm has unilateral incentives to deviate. That means in a sense if nothing else changes, the equilibrium is sustainable in the long run. No different parameters, no different answers.
I would like to elaborate further on your question regarding Cournot and Bertrand. There is something called a Bertrand Paradox in Industrial Organization, which assuming products are homogeneous (that is, if when choosing between purchasing products between different firms the consumer only cares about prices, and no other characteristic of this good) than modeling firm competition choosing quantity (Cournot) and modeling them competing choosing price (Bertrand) will yield completely different equilibria. This had a lot of attention a while back in Economics, but people don't take it too seriously anymore because it requires some very strong assumptions (like if one company charges a penny less than the other, it captures a 100% of the market, so demand is perfectly elastic and consumers have perfect knowledge of prices and no transaction costs) it isn't taken too seriously anymore. Instead, many of the present day applications of the Bertrand model are applied to heterogeneous (other aspects of the good beyond price are taken into account by the consumer, like quality, or simply distinct tastes and preferences) but somewhat substitutable goods (thus there is a cross price elasticity component). Those also have a Nash Eq., and brings forth some really interesting results.