The Comte de Paris on the climax of McClellan's second Richmond campaign

During a recent stay at the Union League Club in New York, I found an original edition (are there newer ones?) of the Comte de Paris' History of the Civil War in America. There is a digital edition somewhere, no doubt, and perhaps I could have read read it on a tablet in a dirty taxicab, but better to browse in a beautiful setting (shown above).

McClellan's second Richmond campaign promised a solid win. The largest-ever AOP had concentrated against Longstreet in the Piedmont near Culpeper-Warrenton, while Jackson's isolated, distant, scattered command scrounged Valley supplies beyond the mountains (the passes of which had been blocked by commands posted by GBM).

While acknowledging the advantage McClellan developed, the Comte speculates on alternative outcomes:

Jackson and Lee, who had a thorough knowledge of the situation, had certainly projected some bold movement upon McClellan's rear similar to that which had proved so successful against Pope ... but they were playing a very dangerous game.*

Strong statements but History lacks notes. Why did the author think Lee had thorough knowledge and a certain plan?

Russel Beatie, perhaps alone among ACW historians, used the Comte's unpublished papers in writing his Army of the Potomac series. Is the answer in those papers?

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* Vol 2, 554-555