Clear Lake's rulings are correct, of course, but, for the uninitiated, let's offer a bit of rationale.
Nothing until A5 fumbles in the end zone is of consequence (except the fact that it is 4th down). Regarding the fumble, 7-2-2-Exception 2 is the "4th down fumble rule," which tells us that only the fumbler on Team A may catch/recover and/or (subsequently) advance a ball fumbled by Team A (before a change of team possession). If any other player of the Team A catches/recovers the ball, the ball is dead at that moment. If the spot of the catch/recovery by the non-fumbler is at or behind the spot of the fumble, the ball remains at that spot. If the spot of the catch/recovery by the non-fumbler is beyond the spot of the fumble, the ball is returned to the spot of the fumble. (If any player of Team B catches or recovers the ball, the ball may be advanced, if not otherwise declared dead by rule (i.e., down by rule). After a change of team possession, the "4th down fumble rule" no longer applies (to either team)).
So, in scenario a) of the given example, the fumbled ball was recovered by a non-fumbler of Team A, so the ball becomes dead at that moment, and is returned to the spot of the fumble. Since the spot of the fumble (now also the dead-ball spot) is in Team A's end zone, the result of the down is a safety, two points for Team B, with a free kick from the A-20 to follow.
In scenario b) of the given example, the ball was recovered by Team B, and Team B has no restriction on where/when they recover the ball. In this case, and on the assumption that B40 was 'down' when he recovered the ball, the ball is dead and belongs to Team B at the spot of the recovery, 1/10. Note that if B40 was still on his feet when he recovered the ball, the ball remains alive and he could advance.
Also, remember, the same rule apples on Try downs (8-3-2-d-5).
