Forrest of course took some number of infantry out with him but it was tough sledding--waist deep ice water or worse--don't know if they double mounted some of them or what. Don't suppose there are any lists of those web footers or any accounts. Am not aware of any other substantial departures although as you certainly know a regiment's roster is rarely all in one place--there is a sizeable component that is detached, furloughed, simply straggling, recruiting or sick elsewhere and these men, once collected together, were often sufficient enough to form a rump remnant. This was done with the Shiloh Iowa left overs but they at least had a rear to regroup in.