> Yes there is. Marijuana is federally prohibited and the form 4473 is a federal form. Per the ATFs package to FFLs Marijuana use of any kind makes you a prohibited person.

Absolutely correct.

You forgot to add that lying on 4473 is a felony, and that the feds love prosecuting anyone they catch doing that, so advising someone to omit their marijuana use when filling the 4473 is basically telling them to ask to be jailed.