Hair Does Not Adapt
Your hair is not "used to" the shampoo you've been using for eight months. It's not immune to your conditioner or de-frizzer. It doesn't care if you use the same great products forever.
There's no evidence whatsoever that hair benefits from changing products every six months. Or every six years. Conditioner isn't an addictive drug; your hair doesn't build up a tolerance to it. If it makes your hair look great, it should always make your hair look great.
Unless your hair changes -- which does sometimes happen. Otherwise, your hair doesn't actually want you to buy the next great salon product every six months. (Although it's perfectly fine if you want to).
Up next: Now that would be quite a trick…