Thanks for going over this.
I want to cover the additional text...
All the copies I downloaded had Moffatt's notes included. Here's what it says regarding the passage above:
That clarifies that these verses at one time in history were considered for inclusion and that's why they were bracketed. Moffatt included them for informational purpose only.
That "(b)" designation I thought was curious. so I looked at the entire chapter 16 of Mark.
The canon part of Mark 16 ends at verse 8. "And they fled out of the tomb, for they were seized with terror and beside themselves. They said nothing to anyone, for they were afraid of — ."
The earliest manuscripts and some other ancient witnesses do not have verses 9–20, but they are in all Bible translations including KJV.
Moffatt had found that there were two possible endings based on the manuscripts available to him, marked (a) which are verses 9-20, and a shorter one (b) "But they gave Peter and his companions a brief account of all these injunctions. And, after that, Jesus himself sent out by means of them from east to west the sacred and imperishable message of eternal salvation."
So with ending (a), Mark 16 would have 20 verses. With ending (b), Mark 16 would have only 8.
So just like with the previous bracketed verses, it was informational.
I hope this clarifies things!
❧