5-year-old Glenview baseball fan wrote every team asking for a pocket schedule. The results have been delightful.

When Mike O’Connor was growing up on Chicago’s Northwest Side, near Harlem and Foster avenues, he collected baseball cards. He’d track their value in Beckett Baseball Card Monthly, which in its heyday, had 1 million subscribers.

Every so often, he’d part with an especially precious one.

“I used...