"IMPORTANT: Tax discs must be surrendered immediately as refunds are generally calculated from the first of the month following the surrender of the disc. A minimum of three unexpired whole calender months must be left on the disc when surrendered."
From: http://www.environ.ie/local-government/motor-tax/refunds/refunds
Link to RF120: http://www.environ.ie/sites/default/files/migrated-files/en/Publications/LocalGovernment/MotorTax/FileDownLoad%2C17194%2Cen.pdf (http://www.environ.ie/sites/default/files/migrated-files/en/Publications/LocalGovernment/MotorTax/FileDownLoad,17194,en.pdf)
Looks like no tax disc no mun.
Garda is just witnessing your declaration is true.