I remember every phone number we've ever had. Even our address when I was 6 years old - 12 NW 72nd Street, Apt D, Gladstone, MO. Phone number 436-7775.
I worked at Service Merchandise in high school (1982). They used a 6-digit number (called an EDP number, for added trivia) for "self service" items. I still remember a lot of those. Glad trash bags? 901397.