I have never danced this dance, or even the one it derived from.
Might I suggest that what you are seeing is due to ambiguity of what you mean to the un-initiated.
If there is an even number of couples, everyone participates in the 1st Pullby.
Then on the Right Diagonal Pullby everyone but the two Men on the ends participates.
Then @ B2b,
"With the one across (opposite sex), pull by left (!) and turn alone"
If I'm across from my partner, does this mean I Pull By?
(I would hesitate there, because single couples at the end don't usually participate...)
It seems pretty clear you do, but again, not knowing I would probably hesitate and that would be
the same as falling seriously behind, causing the next couple having no place to go because there is this couple in the way.
(Hey, I did what you said and stayed where I was...)
This seems a slight case of "Do what I mean, not what I say".
What you didn't say is:
"At the end, if you are facing your partner, you are in for the pullby across."
As for a single couple at the end who wants to join in,
they should be facing each other across the set, next to the opposite sex.