CPL's are in a database with the Washington Department of Licensing along with all the information on the CPL. Look at your CPL, and that is the info that will be in the DOL database. Given a name or a driver's license number the DOL can return whether a CPL was issued in that name or with that DL number used as identification to obtain the CPL. License plates have nothing to do with it, but the officer could call in the license plate number, receive the name of the registered owner, then determine if the registered owner has been issued a CPL.
Further, the DOL also maintains a database of all handguns purchased from Washington FFLs and, given a name or a serial number of a gun, return all the other info, if the handgun was purchased from a Washington FFL.
Some call centers do all this checking automatically. Some do it only on special request.
The department of licensing may keep copies or records of applications for concealed pistol licenses provided for in RCW 9.41.070, copies or records of applications for alien firearm licenses, copies or records of applications to purchase pistols provided for in RCW 9.41.090, and copies or records of pistol transfers provided for in RCW 9.41.110. The copies and records shall not be disclosed except as provided in RCW 42.56.240(4).
Investigative, law enforcement, and crime victims.
The following investigative, law enforcement, and crime victim information is exempt from public inspection and copying under this chapter:
(4) License applications under RCW 9.41.070; copies of license applications or information on the applications may be released to law enforcement or corrections agencies;