The problem is that the code part of the terminology binding:
consists of two parts, the part for the code is of type NAMECHAR which does not accept the characters needed to construct a SNOMED expression.
SNOMED expressions can serve in situations where no concept is available. In this way it is possible to construct any clinical term in SNOMED.
Also I found out that RAED2 codes containing dots are not accepted, like this:
["READ2"] = <
items = <
["at0004"] = <[READ2::9x2..]>
["at0005"] = <[READ2::9NgG.]>
["at0022"] = <[READ2::9NgG0]>
["at0027"] = <[READ2::9NgK.]>