You're questions are good ones, my friend. I hesitate to offer my opinion here because I am still in the learning phase, but part of learning is called discourse (or dialogue) where people speak with each other (not at)... and this post is a great one encourging the good behavior!
Despite my superficial experience on this coin, I see more generally that some coins are 'subjectively demarcated' (in my words) differently than others. Case in point, how many crack stages are there really for 1888-O VAM-1B coins? There are clear differences between the ones that have a crack that doesn't reach the dot to ones that progress to the H10 (Harrison) stage:
http://ec2-13-58-222-16.us-east-2.compu ... -O_VAM-1B4... but are there really 10 or are there an infinite number of them (as any line can be divided into smaller and smaller increments as calculus clearly show us...)? The guide isn't perfect, but it does work to differentiate the stages. In other words, subjectivity can approximate objectivity in some circumstances.
In other instances it doesn't, yet for understandable reasons.
I just submitted a question about a coin that I saw with a new crack on a 1923-D VAM-1AH2 (
http://www.vamworld.com/forum/viewtopic ... 36&p=59731) that could equate to at least one of the Harrison stages/jumps on the 88-O 1B scaling, but was (understandably) told this was not quite up to 'enough' to warrant a 1AH3 designation. I graciously accepted this because I defer to the experts - but I don't hesitate to ask!
The things I'm seeing on this 91-S coin, that to me are minor - interesting, but normal variation. Agreeing that these might be PUPs for some, poop for others, and in-between further still for others.
Nope, I don't believe this answer clears all things up... I hope it doesn't muddy the waters any more, but if it does it may serve a good purpose in the end!