CO gas production rate in the KB Ṁ_CO as a function of time as predicted by our sublimation model (see Appendix A); t = 0 is when the gas release starts, i.e., probably after a few to 10 megayears, and the end of the lines on the right is today. The solid line is for the KB, assuming it starts with a low mass similar to the current KB mass, and the dashed line is for a more massive belt similar to the archetype β Pic belt.