I think both were fine as called.

In the first, it looks like he may have hit the arm as must if not more than the ball. The lead was in perfect position to see it. The camera wasn't.

In the second, the defender never stopped moving towards the shooter. I though it was not a foul from one angle but, as Bad Zebra said, another showed he was moving towards the shooter.

First play: I'll defer to the calling official's angle on the play.

Second play: I hate plays like this where a player hesitates when taking a 3 and then jumps into the airborne defender but I think in this case, unfortunately, it's a foul.

My bad. I meant W35.

I'm assuming in this case the official thought the defense was giving ground. So the defense doesn't have to do anything but play it exactly as he did.
Then the ref decides displacing or giving?

Yup. That's a foul. The defender left his feet and moved significantly forward towards the shooter -- smart play by the shooter to draw the foul.

The overhead shot shows that #1 is probably a miss, but it's still not the look the L had, so who knows what he saw?

Correct -- and I agree with the official that W35 was giving ground and that this part of the action was NOT a foul (and I have no comment on any other part of the play)

Is there a level/age group of play where you might call the offensive player for that much advancement, and contact, as his defender "gives ground."
Does the position of the offensive player's forearm have any influence on a decision to call this an offensive foul?

If the defender is "giving ground", how is that advancement illegal?

Are there any rules prohibiting an offensive player from holding off a defender with his forearm?

I don't think I'd call this at any level I do.

And the position of the forearm can have some influence (but the movement of it has more), but not in this case.

4-24-7 . . . It is not legal to use the hand and/or forearm to prevent an opponent from attacking the ball during a dribble . . ."

I'm looking for input as to how one would answer those questions a) in a setting where newer officials are being trained, and b) when an official is confronted by a coach with that inquiry.

In regards to the forearm, I'm looking for extension and displacement, and hindering the normal defensive activities.

Swatting away the "reach"

Point of the Foul #8. Officials Manual, p. 70.
 

Play 1: Another excellent illustration and reason for high school officials to stick with our own prescribed mechanics versus the "fashionable" fist up and leave trend.

I'm not going to reward an offensive player for jumping into a defender.

the foul was on the player behind A1.

So did B3 have the emery board?