The only way to do such an import at this time would be to do it through an SQL import using an SQL query tool such as phpMyAdmin and populating all fields of the corresponding SQL tables of CBSubs.
Not a trivial task, CBSubs doesn't have only one table like your screenshot shows, but registers subscription, and order/invoice in full details in multiple SQL tables.
It would require to import probably more than what is available to re-create the complete invoice displays that CBSubs does in its history.
Additionally as a non-technical heads-up, re-creating old invoices in a new form is not allowed in most countries either by laws or by accounting regulations. Of course a simple table is ok, but CBSubs does more than the simple table.
2 solutions suggestions:
1) Maybe a freelance developer could do the programming needed to do that particular SQL import for you?
2) If there are not too much users, maybe just do a screenshot for each user's past history in your previous system and attach it to his CB user profile into an image field ?