This could include new customers, and people who were delivered on the 9th. This also eliminates the spiral notebook, and thumbing through page after page after page until you locate that name buried in there somewhere. If you call only to find out that this purchase has to be put off until October. Call her in a couple of months just to let her know that you didn't fall off the planet. She's your client - she bought you.
Some consultants keep a fourth set of dividers on specific product categories.
That way if a specific item goes on sale, they can go directly to that section and see who is interested. Remember to always keep the master copy filed alphabetically. Now as you're reading this are you pondering how you could ever convert all your clients to this new system. This is your company. You can't afford not to.