Can the system keep track of unused airline tickets from my corporate client's cancelled trips so the credit does not go to waste?

Yes, to a point. The system can record that a ticket was cancelled rather than flown and keep it on the corporate client's file along with the traveller name, the route, the airline and the date by which it has to be used again. Your staff can then see what credit is sitting unused before they quote that company a new trip, and you can pull a list of open credits for one client and send it to their travel desk so they know what is available.

How much of this happens on its own depends on the airline and the way you are connected to it. Where the cancellation goes through a GDS or through an API that returns the residual value and the validity date, most of the record can be filled in automatically. A number of low cost carriers and some direct airline connections return much less, sometimes only a reference, so someone on your team has to read the airline's message and enter the value and expiry by hand. The airline's own rules also still apply, including whether the name on the credit can be changed and what fee is charged when it is reused, and no system can work around those.

At the point of rebooking, the system can warn your consultant that a credit exists for that traveller or that company, but actually putting the credit against a new ticket is usually still done in the airline's or the GDS's own tool and then recorded back in your system. Reminders can be scheduled so you are told well before a credit expires rather than after.

It is worth checking which of your airline connections return cancellation and residual value information, and agreeing with each corporate client who decides when a credit gets used and for whom.