Per your second bold, I think the Frank's Memo purposefully conflates descriptions.
The witnesses don't get a chance to clear up any confusion until trial. One switch to the other sketch and BB is referring to old BG for a 10 of 10 match. An attorney in another trial argued before a judge that there was DNA from known SA offenders in the victim's var even though she knew full well they weren't direct matches and the car wasn't even the crime scene. Judge ate it up with a side of fries.
What if the YBG sketch was generated from recall by a friend of Libby's, recalled the individual whom Libby had been messaging? Later discovered/cinfirmed when LE got into Libby's phone which is when LE changed the direction of their investigation. Not sure this theory is supported by what we know but I think we can't trust what's been suggested about so saw what and when.
But I'll throw this out there and contradict my own self -- if BB is the source of the YBG sketch, perhaps his hood, cap, shadowing gave an impression of poofy hair and his agility on the platform gave him the appearance of youth. Didn't seem like a stodgy middle-aged man but a spry, younger one.
So ready for all of this to be cleared up!
JMO