I don't agree that requiring a talisman is irrelevant-- ineptly drafted laws will lack them and fail more easily. The legislative effort to add it may not happen later, especially once judicial review has spoken negatively of the underlying constitutionality of the law.

It also is not of no effect-- it's an element of defense and people have escaped GFSZ act because the government failed to satisfy interstate commerce (and internet search suggests the some courts have taken it to mean that the presence of the gun in the school zone itself must have impacted interstate commerce, rather than just the gun's past purchase did). Every element the prosecution must prove at any level increases the marginal cost of prosecution and makes it less likely to be imposed on more marginal cases.