Parallel running reveals as many problems in the old system as in the new system. Software problems are a useful excuse for project delays but they are rarely on the critical path of delivering business benefit. Business Issues Identify the data owners. Operational responsibilities for the data including executive ownership need to be defined and agreed. Computer salesmen do not provide solutions.
Work is redistributed as a result of implementation.
Design the process taking advantage of the software. You need to change the way you work not change the software to do it the old way. The new system is not a carbon copy of the old system and you should assume that you will need to change not perpetuate the old malpractices. Parameters need to be maintained, with procedures defined and agreed. Set up measures for the data accuracy and control it.