Credit Note sequence problem

This is a slightly larger one. From an accountant that we are talking to, he is suggesting that the current credit noting structure in Civi does not apply to the practice. Credit notes are similar to invoices that need to be hold in sequence in order to keep the correct accounting records. He brought up two possible solutions for this:

1. Credit notes could form part of the invoice sequence and adopt the number which is one higher than the last invoice or credit note issued. For example if a credit note were issued for INV 166 then the credit note number for it would depend on what the last invoice raised was. I.e. if the latest invoice were INV 300 then the credit note for INV 166 would be called CN 301.

2. The second solution proposed was to give credit notes their own number sequence. For example if a credit note were issued for INV 166 then the credit note number for it would depend on the number of the last credit note issued. I.e. if the last credit note were called CN 5 then the credit note for INV 166 would be CN 6.

Option 1 is not an easy one since it is asking to make credit notes independent rows in civicrm_contribution table.

However, option 2 sounds more like a workable solution. This is to either utilise the creditnote_id column to hold a separate sequence just for credit notes and hide the field from the UI. Or, a proper long-term solution is to create a separate table for credit note.

Please note this is a part of the original requirements for VAT and invoicing we set out and agreed with. http://wiki.civicrm.org/confluence/display/CRM/Producing+VAT+invoices