Bigf: You have perfectly expressed my feelings. I too am grateful for the help received here, and have completed the grid - correctly, I hope, though not 100% sure as there are several details which I am not fully convinced about. I won’t go into them now, partly because I don’t feel the puzzle can stand such scrutiny, and partly because I would probably be giving too much away and spoiling people’s Eureka moment. I hope I am not being mean, because despite everything this puzzle has brought me some enjoyment.
In addition to all the weaknesses in this puzzle which have been mentioned on this thread, I feel that the key words in the preamble, MORE and EXPANSIONS, are quite incorrect and do not indicate what was intended. I don’t think I can suggest anything better offhand, but setters usually manage to find a way to “say what they mean” without giving the game away. Thank you, Drxx, for steering me away from extensions without giving too much away!