I hear there can only be one chunk of a maximum of 4 ores. It's possible for them to, miraculously, align themselves with other diamond viens in other chunks to create the illusion of one every large one.
It was my understanding there was one vein per chunk, apparently not. Can someone clarify this?
The world and ore vein generation attempt to be random. The game may average one diamond vein per chunk, but that does not guarantee there is one per chunk.
If you are looking for diamonds check out the branch mining or other mining techniques to improve your efficiency. The number of diamonds you find is typically proportional to how many blocks you can expose in the diamond layers. The brute force method is to just mine out tunnels, but if you find cave systems or lava caverns, it is faster to explore them exposing many blocks at once.
Generally people make 1x2 tunnels in the diamond sweet spot: layers 10-16. Usually you separate the tunnels by at least 2 blocks, so you have tunnel wall wall tunnel = 100% visibility on your walls.
Some analysis of ore vein shape/sizes showed it is slightly more efficient to have blind spots between your tunnels, so tunnel wall blind wall tunnel or tunnel wall blind blind wall tunnel. Veins are rarely completely vertical or completely horizontal, so even if it starts in your blind spot it often exposes at least one block on a visible wall.
Lava fills in most air gaps layer 10 and below, so most don't actively mine below layer 10. Diamonds layer 6-9 are usually too risky or time consuming to pursue. If you are are standing on layer 10 making tunnels, you can find diamonds at your feet (layer 10), the blocks you expose in front/around you in layer 11 and 12, and the blocks above you layer 13. You can then do another branch mine above your lower one, standing on 14, mining 15 and 16, and have 17 above you. Or stagger your second floor of the mine and start a floor lower to expose different blocks on layer 13.