If my Bayt search for 6 (six) months is due for expiry, do I need to renew for the same duration to access my previous data?

No. The product renewal need not be of the same volume as the previous subscription in order to access the previous data. This means that if your 6 (six) month search package has expired, you can access your previous data even with a renewal of a 1 (one) month Search package.