a) month is a long time - if it were tuesday, saying next tuesday is always the next one - therefore “next month” is always the immediate next month.
b) also clear in context - since you’re waiting for the ‘immediate’ next one.
c) to me is the oblique one - since presumably its not tuesday - “next” tuesday should mean the very next one, but depending on proximity to the immediate next one, may mean the one after.
The 13th month is five days long. Squeeze two paychecks in those five days and it would make a dent in the American tradition of spending a months pay you don’t actually have on Christmas gifts.
Next used to be the superlative of “nigh”. (As in, “God is nigh”.) Near was the comparative. So
Nigh, near, next
were parallel to
Green, greener, greenest.
Nigh is now obsolete, and near has taken its place, and nearer invented to fill the missing slot.
So once upon a time, next Thursday would certainly have been the nearest Thursday (probably moving forward, since time is like that.)
But hey, we also have “nearest”, now.
So the meaning of “next” has drifted, and people often use it to mean not the nearest, but the one after that.
But not always. This is still a change in progress.
I’ve had this problem at work. Some people refuse to accept that it can be confusing. I just say, explicitly, “two times per week” or “every other week” or something like that.
Yes, obviously. The point I was making was that your ‘rules’ (this x, next x) don’t actually work as rules. Like just about everything else in English, there is no hard and fast rule for when “next” means the nearest one or the one after that.
“Next Tuesday” is the Tuesday of next week but is said only after the Tuesday of the week before. If you say it on a Sunday, you say “this Tuesday.” On Mondays, you say “tomorrow.”