Obviously the idea behind your rule must be that an EA or FC shouldn't see the book at all, regardless of whether he's alone.
But one thing the PMs probably did think would happen when they passed the law allowing limited use of a code book is that the book would be correct, and not leave people stumbling over "that's not how it is in the book" (I mean regardless of the fact that this particular case was an EA who shouldn't have had it in the first place). From my own experience as an editor of the main UGLE ritual book, I can testify that keeping out typographical errors and ending up with a printed version which actually says exactly what it's meant to say is astonishingly difficult, you really wouldn't believe how difficult it is unless you've actually edited a ritual yourself. After the first few thousand words of proof-reading, your brain starts to go numb, and your eyes slip past an error because you see what you expect instead of what it actually (wrongly) says ... it takes ages to get right. And even then, the printers always find some way to muck up a few details after you've sent them the "final" approved draft. We've never yet managed to publish an edition which was totally free of typos!
On one point, however, I'll offer some reassurance: Bro. Johnnie's worry about an EA reading ahead to things he shouldn't know yet. Our experience over here, having had printed books for many years now, is that when Candidates are allowed to see a book which contains all the work and are asked not to peek ahead beyond what they should know, most don't do it. Most of them are honourable men, after all, and also they do realise that they'd spoil the experience for themselves if they cheated. But yes, occasionally I've come across cases where it looked as if a Candidate had been unable to resist temptation and seemed to know too much ... but only once or twice.
I have a suggestion for you, which might be useful to GLoTX in future, now that you're going down the road of allowing book-learning. Over here, in addition to the normal books which contain all three Degrees, we also publish a couple of special cut-down editions which contain only the First plus the Q&A for the Second, and only the Second plus the Q&A for the Third, so we can give those to Candidates between Degrees without worrying about them seeing anything they shouldn't yet know.
T & F,
Huw