No, that information is false for the most part. However, if Apple introduces new models and resellers still have stock of older models then they need to sell that older stock. It is your responsibility to find out from the seller what the model year of the Mac you are considering is.
Its just like buying a car, if the 2025 models were just introduced and your local car dealer still has 2024 models in stock they need to sell the 2024's. However they MUST disclose to potential buyers which model year the buyer is interested in.
To be honest, I almost ALWAYS buy my Macs directly from Apple. Best Buy and Costco many times only sell the base model of Apple products. Remember its your job as a consumer to determine what your needs are and buy the product that closest fits your needs. Going back to the car analogy, if you need to move a cord of firewood once a month then why would you consider a small 2 seater car just because its discounted??
If the computer is new (yes even if it's an older model) it still comes with a new model warranty and is eligible for AppleCare.