With coins being issued in their billions into circulation, minor errors cannot be checked for removal. Expect to find them, especially in CRH'ing. It can be a happy hunting ground for the enthusiast.
Admittedly, I tend to be a bit lazy when it comes to errors.
That is why I only collect very major very obvious errors, which should ordinarily be removed by machine automatic means, before they are issued into circulation. Perhaps a few of them were deliberately kept aside by Mint employees for various reasons.
The error collection that I have formed consists of brokages, off metal strikes, broadstrikes, piedforts, trial strikes, wrong planchets, planchet clips which are very obvious to the eye, complete planchet laminations resulting in two half pairs, patterns, etc. Because of this approach, I have only about 20 very gross errors from all countries, acquired in perhaps 40 years of collecting. Probably half of them have been acquired on the international auction market.