This query has sat in limbo without response for some time now. This, or at least similar topics, have been visited many times in the past, but every query deserves a response. So...
First off, if you really have completely read through the rule set for "international" snooker, I commend you. I have many times, probably on average about once a year as of late. Your question about nominating the pocket, or potting the ball "cleanly" should be self-evident. Any good rule set (like any good law or governmental constitutional document) should be minimalist in nature, broadly define the objective and primarily concern itself with defining restrictions; that is, the rules should mostly be telling you what you may NOT do. The more the document preaches what you MUST do, the more cumbersome and burdensome it becomes.
The "American Snooker" rules seem to me to be like the rules of Monopoly. That sounds derogatory, but it is not intended to be. What I mean is that, since there is no professional game of American Snooker, there is no governing body for American Snooker, and without that, any rule set supplied is in reality only guidelines from which you can pick and choose your preferences. I relate to Monopoly because everyone that I have ever played Monopoly with will start "Free Parking" with $50 in it and pay taxes and other things into the pot for the lucky "Free Parking" lander to win. Everyone agrees to it, and there are no "Monopoly Police" to verify that you are playing by the "rules" as they are provided by the Brothers Parker .
On the other hand, other than being tinkered with on occasion by the governing body (the World Professional Billiards and Snooker Association), "international" snooker rules are set in stone and clearly defined. These are the rules that must be adhered to by all participants in the professional game. If you are playing the game by anything other than these rules, you very simply are not playing "snooker".....instead, you are playing a modified version of snooker.
To specifically answer your question, "calling ball and pocket" and whether or not the ball falls "cleanly" is a uniquely American concept, presumably dating to original Straight Pool rules and evolving to the braggadocio of barroom patrons imbibing a bit too much and consequently calling something like, "Two-three combo bank, then off the five. It'll do a little twirl, then curtsy before falling in the corner" often with a hiccup in the middle somewhere before the statement can be completed. This type of thing is never required in snooker. A nomination in snooker simply consists of declaring which ball is "on" when required. But, with a nod and a wink to Slick Willie :smilewinkgrin:, you have to understand what the definition of "on" is. So...the "ball on" is any ball or balls which may be legally potted without penalty. If there is more than one possible "ball on", for instance, after potting red or in a "free ball" situation, then the striker must declare, either verbally or non-verbally (through body language/posture....simply whatever ball he is obviously lined up to strike), which ball is "on" for this stroke. If he declares (either verbally or non-verbally) "blue", then strikes blue, it hits another ball, strikes a cushion, then the lampshade, over to the next adjacent table, off its cushion, back to the original table, and falls neatly into the middle pocket, it is scored and re-spotted if required. Despite all else that happened, blue was declared to be the ball "on" (legally pottable) and at the end of the stroke, it nestled snugly at the bottom of the pocket so all is well, no foul has occurred.
The situation to which you refer of a ball falling into a pocket other than intended or falling into a pocket by means other than intended is commonly referred to as a "fluke" in snooker, although you will not find that word anywhere in the rule set. Since the rules are properly minimalist, it is not necessary for any rule to state, "It is perfectly okay for a ball to fluke into an unintended pocket" or anything of the sort. It is not something that is "against" the rules, therefore it is not necessary for it to be written into the rules.
Flukes are something that are accepted by any good snooker player as a part of life although it will still always be like a knife to the heart when your opponent flukes the black to win the frame or match. The consolation of the matter is that, as your game improves, the actual number of flukes that you pot will go down drastically. Not MAY go down, but WILL go down. Professionally, you will see very few flukes. So the next time your opponent flukes a ball, I suggest that you not envy his luck, nor search an avenue to change the rules to outlaw flukes, but instead just think what a great player you must be since the flukes never seem to fall your way.
As for the portion of your query regarding the American Snooker rule regarding flukes, my answer is I have absolutely no idea. It would appear to completely depend on the rules of the house in which you are playing.
EDIT: After consulting the rules yet again to verify, I would like to add to the above scenario of the fluked blue ball.....if you replace the blue jumping up and striking the lampshade with the blue ball jumping up and striking your opponent's skull, and it then rebounds back onto the table, and falls into the pocket, this is also good for a score and re-spot blue as required. No, this is not a foul against the striker. No, nor is it a foul against the opponent struck innocently in the noggin even as he sat away not even at the table. For any who may be interested, the specific rule covering this situation would be Section 3., Rule 10. Penalties, Sub-rule (b), sub-sub-rule (vi) ..."touching a ball or ball marker in play, other than in the lawful execution of a stroke..." . I highlighted in red the words which define that the non-striker in this case touched a ball in such a way so as not to cause a penalty either to himself or the striker.
