Exporting membership data including chosen price set
If I am not wrong - you have imported data from your previous system to civicrm and started using price set. But you couldn't find the old price set in the new system because you couldn't view membership amount in the membership record -- 

This problem is due to data import you have civicrm_membership but you haven't created civicrm_membership_contribution records.

while creating contribution records and line item you will be adding price set Id and price field Id correctly. then this will get picked up in civicrm price set