Stimulated

I forgot to update that Stepdad finally got his Stimulus check. It went to the old house! And apprently sat there, as the new owner was trying to find out how to get it to us through their realtor. I finally got a call from our realtor with a message to call them as the new owner had some mail. Got in touch with new owner who stated she had some mail, including the US Treasury check - she did not want to send it back to them knowing it would get lost in the shuffle and we may never see it! I thanked her many times over and asked her to please drop everything in an envelope and send it out to us.
Now, if we have done a change of address with the USPS, why is mail still going to the old addy? DO these things expire, or is the post office juat another one of these Govt agencies where things get lost in the shuffle? How can you be sure that your mailman is not on Anoretix and something important is going to be forwarded??