You will need a new license number for Solidworks 2017.
You will have a license number for each version of the software. On the other hand, you will have to be careful that the 2017 version points to the 2017 files because sometimes it points to the previous versions.
Either I didn't understand what @ac cobra is explaining or I don't agree.
2 possibilities: - you install the 2 versions on the same machine: just launch the 2017 install by choosing "new install" and it runs by itself - you want to uninstall SW/reformat the machine, in this case see below
The simplest (as I would): - transfer a license with SW2014; - configure your machine; - install SW17 (be careful when walking...) with the license number you have - launch SW17, accept the automatic activation or finish the license transfer procedure (it comes down to the same thing).
Be careful when walking from 14 to 17... By the way, I would be you, I would wait for the SP4 to come out while I was at it. which should not be long in coming.
In 2012 or 2014, I don't know exactly, SW lengthened his numbers but the old ones are valid. By the way, when I entered an old one, it was automatically completed (now I have a table that lists them.
Otherwise, on each of my machines, I have several versions that are all installed with the same number (one number per machine, fixed licenses). By the way, when I launch a new install, it automatically offers me the existing number.