I think the answer depends on what your provider will allow you to do. If you have accounts dating back to 2006, the liklihood that you will collect is very small. You can start with anything in 2006 and write those off. Re-evaulate and then look at accounts from 2007 and do the same thing. The cold hard truth of AR is the older the account/claim, the more difficult it is too collect.
Keep in mind, you didn't create this mess, you are trying to clean it up as best you can. Keep this provider well informed of what you are writing off, so he/she doesn't have a coronary in your office when the AR starts dropping.
Also when it comes to self pay accounts, if a patient hasn't received a bill in more than a year and you start trying to bill them for old services, you better be prepared for a flood of angry phone calls. Put yourself in the patient's shoes, how would you react to a bill from over a year ago. Great customer service sometimes means cutting your loses and moving forward with OUTSTANDING follow up procedures and aggressively collecting on the accounts that are current.
I have been in your shoes many times!! The clean up is ugly but if you use this situation to learn from and how not to make the same mistakes as your predecessors, your clinic will soon shine with current AR and money flowing in that will make your provider quite happy.
Good luck on this process!!