That is the official guidelines that musing curators use.
Of course in conjunction with that document is there own personal opinion.
I believe there are 3 or 4 main fulltime curators and a handful of volunteers that have to sift through all questions and answers to decide which one are worthy of upvotes and at what amount.
Imagine the crap they have to deal with everyday.
People simply spanning the same questions (minor word changes), copying/pasting answers from reddit or quora, trying to decipher broken English or poorly translated English, etc.
Each day more and more people are joining musing so there are more questions and even more answers. There used to be only 50 questions a day with maybe 100-200 answers, in the last week this seems to be averaging closer to 250 questions and 800-1000 answers that they are going through.
I still feel they are doing one hell of a job with all of this. I do worry that musing might turn into the steemit new or trending pages with all the spam crap posts that are just copied from reddit/quora (even questions from certain posters are pulled from there within a few days).
When that day comes I will be sending them a dartboard they can use so they can save what little remains of their sanity.
Fortunately we are not there yet, and the curators continue to sift through all the crap and find the true gems. The ones that impart real knowledge, make people think or perhaps laugh, and are not simply cut/paste from Google or Wikipedia or other similar sources
I'm not exactly sure either but I've seen them vote in new answers to old questions but you have to keep in mind that the curation manpower is limited and things my get lost in the process :-P
I would have to agree with your observations. I've observed that also. I used to think that musing uses bot to up vote good answers and that the bot is programmed to give up vote to good answers at specific time of the day but I've gotten some few upvotes randomly so i don't think that they up vote at a specific time of the day alone. The only issue I've observed is that they hardly up vote quality answers given when their curators are not online.
There''re some good answers that addressed the question asked that got no up vote because they were answered earlier when the curator wasn't active and there are some that didn't address the said question that someone has given a good answer to previously having the upvotes for that question.
Though I'm still new in musings and I'm still trying to understand the platform properly. Only the musing curators can respond to this your question accurately.