SBS 2003 Upgrade Path Questions

I recently accepted a position with a company that outsourced all the IT. Very small company…outsourced company only visisted onsite 1-2x a week.

Here is my question. We are currently running SBS 2003 Premium. The outsourced company did not leave the install CDs or any info about the upgrade they did. The box is all I have and a sticker says it is an upgrade. Now correct me if I am wrong but if I were to restore from a backup I would need the complete upgrade path from the beginning? If they started with SBS 4.5, upgraded to SBS 2000 and then upgraded to SBS 2003 I would need to complete those same steps..correct? I am just a little confused on how this would work if I needed to complete a restore.

Thanks!
S