This sounds more to me like the way to work with the increases on the following row. The pattern seems explicit about the increases which are M1L and R and those are worked between sts.
It may be that you can send a note to the designer or to one of the knitters on Ravelry. The only sweater listed is a cardigan but the increases are possibly the same.
I’ll give it a try on the needles and see if anything helpful happens.
ETA: The M1R and M1L do work although the shoulder sts are quite tight. However, maybe that’s the idea. The tightness at the shoulder will stabilize the shoulder seam and prevent it from stretching too much.
You can see the result in one of the pattern photos.
Hello again,
Thank you for your explanation ! It works Out well!
I started knitting in the round however I’m wondering …
For the front it Said that every first and last st are K sts
knit back and forth in fisherman’s rib on needle 9 mm over the 49 (55) 57
(61) front-sts, except the 1st and last st, which are k sts on every row.
When knitting in the round the first st is now a K sts , should I do the same thing as when knitting back and forth which is to k 1st and last st or should I purl before k1b ?
If I start knitting k1b then purl, the pattern will change however it is said to knit in Fishermans rib 1st and last st included
Knit in fisherman’s rib over the 49 (55) 57 (61) front-sts (1st and last st
included), cast on 3 new sts under the armhole opening.
And at the beginning of the explanation of the pattern it is said that for 1st row we should start with k1b:
1st round: k1b, p1 repeat from - the complete round.
2nd round: p all sts.
Should I start knitting in the round by a P or K and then k1b? 
Thank you very much !
When you’re knitting back and forth it’s very difficult to work the first stitch or the last as k1b. That’s why the Fisherman’s rib knit flat keeps the first and last sts as knit or stockinette sts. This also gives a nice edge if you have to seam.
Working the k1b at the beginning or end of a round isn’t a problem. If you can keep to the rib pattern and work the k1b then go ahead and do that. When your pattern says 1st and last st included it may be referring to the stitch count. At any rate, you want to keep the pattern stitch aligned with previous columns of k1b and purl.
I’ve placed 2 STM as followed:
Knit in fisherman’s rib over the 49 (55) 57 (61) front-sts (1st and last st
included), cast on 3 new sts under the armhole opening. Place a stm centre
between the newly cast on sts. This stm marks the left side seam.
Continue knitting in fisherman’s rib over the 49 (55) 57 (61) back-sts, cast on
3 new sts under the armhole opening.
Place another stm centre between the newly cast on sts. This stm marks the
right side seam and the round’s beginning for the rest of your work.
To knit decrease:
Knit 3 sts in fisherman’s rib (incl. the marked st).
Slip 1 st knit-wise, but into the st the row below. K2tog (k the left of the two sts
into the row below, the right st regularly). Pass the slipped st over.
Knit in fisherman’s rib until 5 sts before the marked st.
Slip 1 st knit-wise, but again into the row below. P1. Pass the slipped st. Now
slip the st over onto the left needle and pass the following st over this st, once
again, from the row below.
Knit in fisherman’s rib until the marked st.
Repeat from - and continue knitting in fisherman’s rib until the beginning of
the round.
Is there 2 decreases per round ?
When it says knit in Fishermans rib until the marked st is it the STM that marked the beginning of the round?
There are 4 decreases per round. The first is a slip one knitwise, k2tog, psso (2sts decreased).
The second is a slip one knitwise, p1, psso (one stitch decreased) then slip the stitch back to the left needle, pass the next stitch over this stitch (the second decrease) and slip the stitch once again to the right hand needle, then continue in fisherman’s rib.
You have 2 side seam markers. The pattern locates the beginning of round marker at the right seam marker between the back sts and the front. (I have a quibble with the pattern here. If you are knitting in the round and this is the pullover version, the knitting across the front should take you to the right side seam not the left side seam as the pattern says. The beg of round would then be at the left seam marker. )
