When you switch from one computer system to another there is no need to trash the old system once the new one is in place. Keep it up and running. That does not mean you do dual entry and try and use both systems simultaneously, that’s a sure recipe for disaster. Set a day to “go live” with the new system and just do it. Keep the old system available for looking up old information, like last year’s treatment or what the insurance paid six months ago. That’s why you don’t need to transfer every piece of old data, you can always access it from the old system. You will find the need to look up information in the old system will quickly pass and you will rarely access it after a few months. None the less it is there as an archive.
You will probably use the old system for continuing care recall for the first six to twelve months as people and information are added to the new system.