It’s a good idea to reveal the Revision number by serial number, but that information is only in the Purism database.
It would be great if Purism enabling REV NUMBER CHECK on Purism Website. @Kyle_Rankin
Yes it is printed in PCB, check the picture above. But not worries to much for ECO revision GNSS fix, all Evergreen batch the GNSS work good it just that on last revision batch the g.n.s.s got better sensitivity. I guess that serial number L520#### it is for Rev1.02-1.03 and L521#### it is for Rev1.6.0.1