Red oaks do take 2 years to mature. While a tree has immature acorns that are still under development, they will also have mature acorns ready to drop.

It is as if they have two generations of acorns on their limbs at the same time, if you see what I mean.

That way they almost always drop acorns every year.

There are always acorns still under developed and still growing at the same time that there are fully developed acorns ready to drop.

The white oak doesn't do that. Its acorns develope and fall in the same year while the red oak take two years to develope but the previos year's acorns fall that year.