Wait, are the commercially licensed icon sets also open-source? If not, then the title is too misleading IMO. I don't think it took you 12 years to create the free icons right? It took you 12 years to create all the icons (free and commercial).
We create, refine and improve our icons over time. Some of the open source icons have been improved 4 times over the course of 12 years. Not all sets are open-source.