Setting up a system for regulating the "manufacture", distribution, and sale of ganja and ganja products in a year has proven to be problematic. Consider, for example, the variety of conflicting laws across the United States regarding alcoholic beverages. Three counties tried to opt out of the regulatory scheme, at which point the DoJ demonstrated absolutely no interest in prosecuting the pot smokers of Yakima County.
There are numerous surprises and complications which have not been resolved. For example, both Colorado and Washington have assigned the regluation of ganja to their liquor control authorities, which makes sense. However, they have a history of operating under the 21st Amendment of the U.S. Constitution, which leaves the regulation of alcoholic beverages entirely to the states (It's why in some states titty bars are prohibited from serving booze--States can ban First Amendment protected activities from certain buildings if the buildings serve loquor.) Part of the agreement the DoJ made with Washington and Colorado was that the states would actively limit distribution to within their boundaries. But there is a long history of cases which prohibit limitations on interstate commerce, except for the 21st Amendment. One possible resolution is for the feds to classify ganja as an "alcoholic beverage", which makes a lot more sense than its present classification as a "Schedule I narcotic".