Let's break down the title BS 5839-1: 2017. This means British Standards 5839 Part 1 Version 2017. British Standards are being amended all the time and as such it is important to always refer to them with the version attached, usually this will be the year of the last major amendment. When reading online or through the paperwork of a fire company you will often see the tile without the version, and this is to save the need to update things when a new version is introduced. Technically, it is always the latest version that is bound to be followed.