Gee Mike, only once? I may have done it twice.
Last time I poured another powder on top of it and had to pour it all into my "fertilizer" can.
Even if I knew what was in it I don't think I'd use it because my powder measure doesn't seal well. Like you, I seem to catch mistakes when I clean up and I clean up before I load so I haven't had any powders make it into the wrong cartridges, even when I dump the powder into the wrong can. Yep, I use the most expensive fertilizer on my block!