The PC speaker is normally meant to reproduce a square wave via only 2 levels of output (the speaker is driven by only two voltage levels, typically 0 V and 5 V).
For example, if your payments for March and July 2010 were each one month late, the report may continue to show (for seven years from the date after each payment was due) that you were 30 days late twice in 2010, even though the tradeline for that account also shows your payments for the rest of 2010 were made on time.
Late payments are black marks that normally stay on a credit report for 7 years. That's true of most negative information like foreclosures, Chapter 13 bankruptcies, charge-offs and paid tax liens; a Chapter 7 bankruptcy stays around for 10 years and unpaid tax liens can linger indefinitely. Late payments and other negative items that are several years old aren't as damaging as a recent report.