The overall argument you tried to make was that MS or Sony might know enough of their competitor's specs early enough to be able to adapt their own offering and guarantee a performance advantage.
Your example with MS using the PPE as a basis for Xenon is a poor example. MS might well have known some details of the technology Sony would use, but that provides no indication of overall performance and thus provides no basis for MS to change or adapt their design to guarantee a perf advantage early on.
18mnth prior to launch isn't enough to change anything either, especially when you consider that 8 months of that would have been volume production of units to stockpile inventory ready for a simultaneous worldwide launch.
Specs get locked in 2.5 to 3 years in advance, with the exception off-die factors like memory quantity and APU clockspeeds.
This is the first time I've seen that mentioned, previously it's been 2 years was the stablished understanding but even then we know things can change late on (for simple upgrades like the RAM thing) - and OOI do we know when Sony went from 2 cells to Cell + GPU? Also, worth questioning the 2-3 lock in because IBM went to MS in 2003 and X360 was released in 2005 so...yeah, 2-3 years is bit of a stretch maybe?
Maybe it was a poor example - I was just using it to show that information gets out, and sometimes very detailed and important 'secret' details get passed to competitors. I think this gen (PS4/XBO) a similar thing happened, an example, I think Sony got wind of the MS 'always on' and 'disk licence' fiasco and used that to their advantage. I also suspect Sony may have made is seem their machine was less powerful than it actually was...I seem to recall a guy I worked with being confident that XBO would be more powerful based on rumours he was reading before the real leaks started.