You could also set up a table that links to the user table (if u have one) and could set an application status of sorts, whether it was a trail version, even the level operability based on the licensing package they bought from you.
for example :
tblUser_License (this links the user table to the license table)
idUser(int)
idLicense(int)
tblLicense (this holds license info)
idLicense(int,identity)
vcDescription(varchar 500)