For 9 versus 7, 2 cards (I took an average of the EVs for 4-5, 3-6, and 7-2)
I have EV(hit) = 0.152 SE = 0.0004
EV(double) = 0.142 SE = 0.0008

which is pretty much the same as you.
(Of course, with up card 7, 7-2 would occur slightly less often than 4-5 and 3-6, so it's not perfectly correct to average the three EVs, but the hit and double EVs would have to be infinitesimally close for something like that to actually matter.)

I've corrected all this in my book, and am currently uploading it to the publisher's server (which takes about 4 hours). So anyone who buys the book from tomorrow will get the correct strategy.

I ran the strategy through the house edge calculator and it makes virtually no difference to the house edge. Obviously this is because the hit and double EVs were so close, and 9 versus 7 is not the most common hand.
The good thing is that it means that the error won't afect anyone financially.

Obviously I have to redo my indices. I'm running them overnight, and will upload them to the publisher's server. So to anyone considering buying my book, please wait for 2-3 days to give me enough time to update everything.

For people that already have the book, I will post the indices on this site, plus I will post an Errata sheet on www.spanishcountess.com.

The win rates and SCOREs will probably be unaffected as the two plays are so close in EV.

And to MGP, thank you again for being such a good bloke about it (as we say down here). I only wish that I'd had someone like you to check all my work when I was writing my code and writing my book. It would have saved me months of work.