both results of [x rounds swiss pairing system] and [+1 round] are used in
(3) up and down by maximum 4 positions with ...

after the [x rounds swiss pairing system], the ranking results of Top 8, say A, B, ...H will follow the pairings below for [+1 round] : --

A vs H
B vs G
C vs F
D vs E

and assume H, B，F and D win in this [+1 round],

A vs H (w)
B(w) vs G
C vs F (w)
D(w) vs E


then the final ranking positions are : --

1 B win
2 D win
3 F win
4 H win
5 A
6 C
7 E
8 G

i.e. the winners B D F H and the losers A C E G use the ranking results from the [x rounds swiss pairing system].

You can look at it from the table below : --

5A move down 4 positions
1 B (win) move up 1 position
6C move down 3 positions
2 D (win) move up 2 positions
7E move down 2 positions
3 F (win)move up 3 positions
8G move down 1 position
4 H (win)move up 4 positions

It is logical for winners of [+1 round] to move up {maximum 4 positions} and losers of [+1 round] to move down {maximum 4 positions}.

Since this is critical [+1 round], could have 分先 if time permits, the concepts of winners in Top 4 and to be promoted still maintain and

do not need to play two more rounds ( as in x + 3 system )

since the [x rounds swiss pairing system] should carry weights in the final ranking for positions 1 to 4 and 5 to 8.