The prefix was associated with certain network licenses (also called "SNL" – SolidNetwork License) or specific promotional educational builds. In some very old versions (SolidWorks 2007–2012), a serial starting with 9020 might have activated a student edition or a 30-day trial.
If you have an old version of SolidWorks installed, use the SolidWorks Installation Manager to "Change" the installation and update the serial number rather than installing fresh. solidworks student serial number 9020
If you still find a website claiming to offer a working 9020 serial, here are red flags: The prefix was associated with certain network licenses