You can use the existing number you just need to patch up the rest of the missing parts.
Tables included will be 38 and 39. 38 is the parent table and the unique reference to an entry is “Document Type”, “No.” so for you this is Invoice and your existing no. 39 then uses this logic “Document Type”, “Document No.”, “Line No.”, so for you that is Invoice, existing invoice no. and possible a number you have for the details of the invoice. If you don’t have one then use a value. BC typically starts line numbers at 10000 and goes up in ten thousands. You don’t have to stick to this but it’s standard for a reason.
Note that you have to post the invoices again as opposed to importing them straight to the posted invoice tables which have different table id references.
If this method is still not working out you can revert to a 1 dimensional structure. Use the purchase journal and entry 1 line per invoice for the total value with the corresponding dates. If you have an attachment use the incoming document feature. Balance it to the accounts payable control account.
