The number in the Rev column is how many times, alphanumerically, somebody decided there was a better way to do it. As Bones said in Star Trek the Motion Picture, enginneers are always changing things.
The number in the Rel column is how many pages, and what size paper the drawing is on. A T means it's either buried in Deborah's file cabinets, or is buried on someone's desk.
The number in the Quan column is how many we need. This number often makes little sense knowing that we undoubtedly need more than one database, or any particular drawing for the entire project.
The final column is the description of what the document/part is/is about.