It's all about context, for my money. A couple is always two, I'll grant that, but with the others...

If the subject is "continents," then six would be "several." However, if one is talking about grains of sand on a beach, then I'll grant that six is only "a few." Or is there anyone here who wants to argue that six grains of sand on an entire beach constitutes "several?" ;-}

If you're going to demand an exact figure (and I'll assure you that I don't follow this as any sort of rule), I'll say that "a few" is anywhere from more than one up to about forty percent of the rough entirety of whatever is in question, after which it becomes "several," and continues in this fashion right up until "all."

Dar "several bricks short of a full deck" ien