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.
If you miss a payment (even just one) on one of your credit accounts, the late payment could remain on your credit report for up to seven years. If you fall in the habit of paying late, your account could be charged off or sent to collections, which could further dent your credit score.