Not always, but that depends on the design and end-use of the printed circuit board (PCB). Solder mask (also called resist and overcoat) is used to isolate conductive areas of the PCB by covering them with an insulative layer. It also stops solder from wetting (flowing) beyond contact areas, so prevents bridging and other soldering defects.
The shelf life of a product can be found on either the technical data sheet (TDS), available on the product page or by looking on the certificate on conformance (COC). The COC can be downloaded by going to https://www.techsprayeu.com/coc. Once you have the shelf life, you will need to add it to the manufacture date for a use-by date. The manufacture date can be identified by the batch number. The batch code used on most of our products are manufacture dates in the Julian Date format. The format is YYDDD, where YY = year, DDD = day. For example, 19200 translates to the 200th day of 2019, or July 19, 2019. This webpage explains and provides charts to help interpret our batch numbers: https://www.techsprayeu.com/batch-codes.