I agree with Solitary Man - up to a point. As for failures with cases, usually they can be prevented by careful inspection of each case, after cleaning and sizing. Incipent case head separations or neck- splitting is usually easy to spot.

Having said that, I will reiterate that I do agree that it is best not to mix up batches of brass. Besides the failure issue, if the brass is all mixed together, it's hard to have any idea of how many firings one is getting from a case....and indeed when it is likely that a case is about at the end of it's useful life. It's not difficult to keep the batches separated - it simply requires a little more care - and perhaps a bit more record-keeping. I separate my brass into different gallon-size ziploc bags. I simply mark the outside of the bags with the number of firings..and any other pertinent info. When reloading, I keep each batch separate, by pulling from each bag separately....and placing the finished rounds in different ammo boxes, with appropriate markings. I also attempt to cycle through all of my brass, before re-firing any of it (for example....I have 215 cases. I try to fire all 215, before I fire any of them a second time. I reload pretty much after each trip to the range - but I rotate the cartridges so I am always using the "youngest" brass first. In this way, I am able to keep my brass (mostly) all the same "age". This does not always work, but I try.)