The general/sales/purchase journal pages do not base on different tables.
They all base on the same table (ID 81)
And in order to get historic "transactions" into BC the recommendation is always to register /post these, using the BC standard posting routines, with all the necessary validations, for example for debit and credit consistency, in total, per month, per day, per transaction ...
Important field values will be created only with a proper posting, like the right order on Entry No. and the Transaction No., which can be important for future actions
For the subledger, like receivables and payables you should at least take over the individual "open" entries with the remaining amount and some important information like Posting Date, Document Date, Due Date, Payment Discount Date, Payment Discount Possibel (amount), External Doc.No. etc.
For fixed assets you should take over the accumulated historical acquisition costs and the accumulated historical depreciation amounts (with a posting date = last date of the previous fiscal year)
For the general ledger / G/L accounts you can take over the balance (for example with a posting date = last date of the previous fiscal year), or you can take over amount per month (that would allow monthly comparison in BC: month X current year vs. month X pervious year)
But all entries should be created by "posting", not just directly "written into an entry table" !
