Also, in

(define-public icedtea-6
  (package
[...]
))

"icedtea-6" is a variable name (in the programming language Guile).

The package name is there:

[...]
(package
  (name "icedtea")  <-----
)

We don't have version numbers in package names--but you can request
a specific version by 

$ guix package -i xxx@1.2.3
                  ^^^ ^^^^^ package version
                  package name