Do we have to get the TIN certification completed on customers who have already provided a W-9? If they open a new account or make changes to an existing account and if the original account was opened prior to the 2001 change regarding cerifying that you are a US citizen? OR is getting a TIN certification one time all that is needed.

A W-9 remains valid forever if properly completed, unless you receive a notice from the IRS that the name and number you are reporting on form 1099/1098 (etc.) don't match.