When Holmes Basic was published, 1977 to 1980, polyhedral dice were something of a novelty, and TSR had some trouble maintaining a steady supply. Many of the Basic Boxed Sets came without dice, and so a cardboard insert was added with cut-out chits to take the place of dice. Instructions were provided on their use (see the pictures above) which also included how to use the dice once you had them.
Strangely for a set that was aimed towards beginners, John Eric Holmes provided no details on how these funny little pieces of polyhedral plastic were to be used. The d20 was marked 0 to 9 twice, and was to be used as a d20, d10 and d%, but how was one new to the hobby supposed to know that? It's a glaring mistake on JEH's part, and TSR, and details on the dice had to be added to the back of the last page, plus on the chit insert.