So my understanding is first touching can occur either in flight or after grounding on scrimmage kicks. In any case my understanding is that R can never advance a ball if a fair catch signal is given.
I wonder if this is a newer rule to avoid deception by R; where 2 receivers are back and one is waving his arm and yelling to draw the attention of K...yet the ball is going to the complete opposite side of the field.
This has been the rule for as long as I can remember. I was taught to think of the "Fair Catch" as an agreement, binding on both K and R, triggered by R's signal. R agrees to NOT advance the ball (by ANY/ALL member of R, after catching the ball), ANY member of R, who actually signaled for a Fair Catch also agrees NOT to block K, until the kick has ended.
In return for forfeiting their right to advance the kick, R e xpects K to provide an unmolested opportunity for R to catch (move towards) the kick after ANY R player giving a valid, or invalid signal. (NFHS 6-5-3:" Only the receiver who gives a valid signal is afforded protection. If after a Receiver, the catch is made by a teammate it is NOT a FC, but the ball becomes dead."
NFHS 6-5-6: "This prohibition applies even when no FC signal is given, but it does NOT apply after a FREE kick has been touched by R, or a scrimmage kick has been touched by R who was clearly beyond the neutral zone at the time of touching. (EXCEPTION- which is relatively new- K may catch,touch, muff or bat a scrimmage kickin flight beyond the neutral zone if no player of R is in position to catch the ball."
Kicking Table 6-4: Scrimmage kick 1.Kick recovered beyond the NZ may be
advanced ONLY by R
(As long as it's STILL A KICK).
Free kick 3. Kick can
NOT be advanced by K.