Here is a practical question - and I'd be interested in any views, because it is one of those things that don't get taught in library school but I bet we face quite often in the workplace.
As I have said before, much of our straightforward cataloguing is delegated to library assistants - who have no theoretical training in the rules of cataloguing and indexing and, very often, no previous experience. Their job is to download records, check them against the book in hand, identify errors or omissions and make any necessary changes. They deal with (what should be simple) adult and children's fiction, all English-language and all of it newly, or recently, published.
Were they professional cataloguers, I would expect them to know AACR and M21,
and apply those standards sensibly - by which I mean, that if faced with a record acceptable in all respects except a fairly minor one (and I mean something like the omission of "by", or an ampersand for "and", in the statement of responsibility) then I wouldn't expect them to correct it. On the other hand, I would expect them to put right something that really matters - a mis-spelling in a name, or an added entry omitted. So they have to know what matters and make a judgement - is it worth spending time correcting or adding something if it doesn't affect retrieval and isn't misleading, bearing in mind that we none of us have time to do everything perfectly and their time would be better spent on something more important.
That's a fair enough expectation (in my opinion) for a professional cataloguer, but is it fair enough to expect the same of a library assistant? I find it quite difficult to explain the rudiments of AACR and MARC to library assistants, but they will usually believe me that there are rules which should be followed. What they find very hard to understand is when rules needn't or shouldn't be followed.
What I tend to end up with, therefore, is a simplified set of rules being rigidly (I could almost say, thoughtlessly) applied - which is not much to the benefit of the staff or the catalogue. I don't like people using tick-lists but I am often told that this is easier and that it is unfair to ask library assistants to do more than this.
What do other people do?