Castling Rules-Does “The king & rook must be on the same rank.”="Only original rooks can do castling."? According to Wikipedia, one of the conditions of castling is:


  The king and the rook must be on the same rank (Schiller 2003:19).


This is because of a loophole that would occur otherwise:


  Without this additional restriction, it would be possible to promote a. pawn on the e-file to a rook and then castle vertically across the board (as long as the other conditions are met). This way of castling was "discovered" by Max Pam and used by Tim Krabbé in a chess puzzle before the FIDE rules were amended in 1972 to disallow it. See Chess Curiosities by Krabbé.


I understand this rule like this: Only the two original rooks (not promoted rooks) can partake in castling. Is there any loophole in this understanding of mine?
No.  You got it right.  

The King can only castle if the K and R is on its original square and each has never moved,  the king is not in check, and the king does not move through a check, and it is your move so you can move. 

I remember that puzzle. Guy at worked showed me a mate in one.
Which was impossible.  I finally guessed he was a true patzer and thought you really could castle with a promoted rook on the king file.
So I did that and got the puzzle right.  

It was hard to conceive of castling that way but the rules got fixed to make sure it would never happen.  As if it could happen in a real game and not a puzzle-problem.