Hi
Yes, it is really necessary to reflect and do consistency check in production version for latest BOM update.
Impact on production order:
If the updated BOM changes are not reflected with production versions, and if any of the planned orders which are created in last planning run, then these planned orders are having bom explosion as per previous to the change you made and this reference is taken from production version.
When you convert planned order to production order, same component list with quantities copied to production order.
This will not help you with your changed BOM. So when ever you update production version, and rerun planning and old planned order are not firmed, then they are deleted and recreated with new PV and new BOM details are copied.
Impact on Costing:
If your order has BOM with production version before you change, then the actual components and quantities if at all you changed in BOM, that will not reflect in orders. This results is not having actual cost to the order, if at all you do goods issue which is unplanned then the cost get captured in order, if you do GI against order.
And this result in more variances for order.
Hope above answers satisfy your question.
Regards,
Sharat