I heard one can get a better deal on a new car at the end of the season (i.e., calendar year) before the next year's model arrive. What kind of reduction percentagewise can one expect in such sales?
Manufacturers sometimes give incentives to car dealers to ensure that the prior year models are sold out before the year is up. However, dealers are usually pretty smart on only ordering the cars they know they can sell before this happens. Also, manufacturers are usually pretty good about only producing enough vehicles to cover demand.
Honestly, you aren't likely to see these incentives materialize unless the manufacturer really screwed up.
If that happens then three things occur. First is that manufacturers give a hidden incentive to the dealers. Dealers won't publicize this, even internally. If the cars are still not moving after a month, then the dealers will tell the salespeople that those cars have a specific "bonus" on them. If those cars still don't sell, then the bonus inflates quite a bit and dealers begin advertising that car at a deep discount on the radio. It's pretty much guaranteed to sell at that point.
Barring those circumstances, the deal you get on a brand new car, late in the model year, is likely to be the same you could have gotten early in the model year.
Honestly, if you want the best deal possible, look at the date of the inspection sticker on the car. If it is close to the 3 month mark then the dealer will bend over backwards to sell the car as the finance costs are racking up on it. They'll often sell that one at heavy discounts.
It completely varies by manufacturer, dealer, and time of year, but in general yes, you can get a (sometimes significant) discount on brand new last year models.
In general though, it comes down to supply and demand.
As an example, in April 2016 I was looking at a brand new 2016 in which the 2017 model had come out that week (I thought April was a little early for next year's model but sometimes that's a marketing tool). The sticker price of the 2017 was only $100 more than the 2016, but the 2016 was selling for $3K under MSRP, and the 2017 was selling at exactly MSRP since they only had 2 in stock.