What differentiates them is what level they are at in their reading and collecting pastimes. Readers of collectible romance should only purchase those books that are at minimum a C in grade. This means that there are creases in the spine and maybe on the tips of the cover. Basically, it is a readers copy only. At this point, many readers would like to get their hands on even a C graded copy of Mackenzie's Mountain.
Collectors typically hunt for mint to near mint condition copies of their favorite books.
They are grades A and B respectively. An A grade is basically an unread book. No book store stamps on the edges, inside the front cover, etc. The book is as close to perfect as possible. These are typically very difficult to find for older books written in the 1980s and near impossible for those in the 1970s and earlier.