Hello and welcome.

The mint ships out new coins to the banks via the armoured car companies. The companies, however, will ship whatever coins they happen to have on hand at that moment to the banks when the banks ask for coin - and that might be new coin, it might be old coin, it might be a mixture of both. It's basically pot-luck whether or not you happen to find a bank that's got a shipment of fresh coin.
The coins they put in "mint sets" are not production-run coins intended for circulation - they are made specifically for placing into the mint sets, and those are usually made the previous year so they can have the sets ready for sale in the leadup to Christmas. If you want production-run coins made in the actual year stated on the coin, you have to obtain them from the banks.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis