The upgrade rules for tiles in 1829 are meant to be inherent in the tiles and therefore intuitive. I829 does not encourage an interchangeability between junctions and destinations until the russets, while 1830 would have done so in the greens had the concept survived. That reverses the 1829 philosophy of dealing with dots in phases one and two and building on the result throughout the game. Clearly, any distinction between city tile functions are irrelevant in 1830. Economic growth is the only measure of an 1830 city tile's function.
All open circles are future junctions which make money.
This is perfectly acceptable in 1830 because of the game's theme. It is a severe and cutthroat game and can only be played that way. It is the classic of the genre because of its simplicity. The problem is that 1830, not 1829, became the standard for 18XX game design in North America. Having only K and X tiles results in the same economics as 1830, although the ability to upgrade dots is a great improvement.