smellyharry, once you have the theme and are looking for types described by the previous words in the quotation, there is a very limited set to look for. Once you find two, they don’t even have any letters in common with the remaining possibilities, and knowing the length of the last item we can spot that it contains one very noticeable letter which, as it happens, only appears once in the grid. We can quickly see that although the word can be sort of discerned in the vicinity, it is not in a form that fits the instructions.
I agree that the last time is “fair” and indeed I can see that some care has been taken in drawing up the preamble to make sure it is scrupulously so. However, I’m not sure I see the point of it: it doesn’t add to the puzzle, and isn’t particularly thematic. I think a gimmick like this is best kept for when it specifically amplifies some thematic aspect in a clever way.
polyn, I too cannot see any other occurrence of any item except the three I think we are meant to highlight. You’re either being sharper-eyed than us or are thinking along a different line altogether. However, we can imagine a situation where we are to highlight a word in the grid and the word appears twice through some carelessness on the compiler’s and editor’s part — in that eventuality, I’m sure highlighting either of the two cases would be accepted. If you think you’ve found an alternative, by all means highlight it to see if it’s accepted! But take care to really check that it matches every part of the carefully-worded preamble, because I can’t spot what you mean by that.
PS no, I don’t think we have any assurance that anyone particular monitors this forum. It’s for us to discuss and help each other. Some setters do look at it, and sometimes join in with discussion. But nothing is guaranteed. If you wish to make a view known to the editor I would write to him.