If the serial number is missing from your upright piano, you can approximate its age by examining its design details. In some cases, pianos that are missing serial numbers still have their case or parts numbers, which can help to identify an instrument's year of manufacture. You can also perform a more careful search for the number, checking five key locations on the piano.
Piano serial numbers are not always easy to find. Many upright piano serial numbers appear on the instrument's gold harp or plate, which is located under the lid. If it is not there, check for a number plaque on the ledge beneath the lid on either the left- or right-hand side. Some numbers appear on the top of the wood frame at the back of the instrument or on one of the hammers or keys. If you find the number, compare it to the production years for the major manufacturers, including Bechstein, Kawai, Yamaha and Steinway.
If none of these locations reveals a serial number, try to identify the manufacturer. If the piano is a Steinway, it bears the label “Steinway,” “Boston” or “Essex". Steinway pianos also bear patent numbers particular to the manufacturer; if your piano's patent number matches a Steinway number, it is a Steinway. Often, the name or names of makers appear on the inside of the instrument. If the piano has no maker's mark, photograph it to gather manufacturing details. Compare these photographs to pictures of pianos with known provenance, or enlist the help of a piano craftsman or auctioneer to appraise the instrument.