The commentary in the handbook is not enforceable. The other text is exactly the same as the plain code book.
But although it is not enforceable, it may be
considered when arguing about wording in the NEC itself whose meaning is in dispute.
In a very loose sense, expert testimony which can be supported or refuted by other evidence.
Just as the Supreme Court looks only at the law as written, but still may
choose to look at the recorded intent of Congress as reflected in the transcripts when considering what the words mean. The transcripts of debate cannot change the effect of the law when the wording is clear, but it can guide interpretation of unclear wording if the Justices are inclined to do that.
If the wording is unambiguous but also clearly not what Congress intended, the best that the Court can do is suggest that Congress amend the legislation to fix the problem.
One example is found in the Supremes' consideration of the Defense of Marriage Act. The supporters argue that the Act was just a reasonable and non-discriminatory use of the police powers of the State.
Opponents argue that the Act, although it does not say so in so many words, is intended to punish gays.
The record from the floor of Congress shows the leaders of both parties praising the fact that the law "sends a message to gays that their lifestyle will not be tolerated."
Ooops.
Not enforceable, but not to be ignored either.