Thanks for the suggestion cblaisd. From a link in this archived post:
Certificates vs Vouchers guidance - a resource:
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">
Type A - Discount Certificate
The authorization to issue a ticket at a reduced amount using the discount certificate as support.
Type B - Voucher
The authorization to issue a ticket at the full value with the value of the voucher used as partial payment.</font>
If a Service Check voucher says on it "Treat as Type AB Certificate", what does that mean?