GDR1 is not, MS ditched that with 8.0 GDR2, instead calling GDR3 "Update 3." although many use it, and we know what it is.
Lumia Denim is not Windows Phone 8.1 Update 1, it is a firmware package that is associated with 8.1 Update 1 and does not apply to non-Lumia phones.
Just minor things, I know, but just for info's sake.