That earlier error was also partly the result of miscounting the number of six-letter words right at the beginning, making me think the unclued entry must be six letters or a six-letter entry appeared in the centre. Had I not made that careless blunder I might have made quicker progress earlier.
My highlighting would appear to be different from Orson's. I have four, not five blocks of cells, 14 cells altogether. I can see another arrangement involving 15 cells but it would mean that the two items wouldn't really match each other in their mathematical representation.