Do model years that can be before the actual calendar year for delivery dates have anything to do with vehicles that are listed on IMCDb?

We generally use what each manufacturer applies. Most cars introduced late in the year are generally regarded as next year's model and are identified as such, either by sales literature or the 10th digit their VINs (or immediate digit for older cars).

Some exceptions to model years are present, notably JDM and AUDM cars (cars of Japanese and Australian origin sold in their respective markets).

This is a rather useful answer, given that I have mistakenly mislabeled certain cars and their model years and such. Thanks, Lateef!