Mapping old data in SAP??

Hi ALL

In our organization SAP has implemented just few mnths back.So, now client rqmnt is to have all the PRs, POs & GRN in SAP those which made in TALLY before SAP implemented and all the cost should be booked in the past date..But doing all this activity is not an easy task b'cos we have almost 30 projects running presently....So , pls anybody suggest me the feasible & easier way to do this ....

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Thanks

Vikram