Dont understand :-(

Hi,
Could someone clarify the following pleases, as I don’t understand how i’m supposed to’keep continuity of stitches’ if i’m supposed to increase at the beginning and end:
'Setup Pattern
Next Row (Right Side): Begin St st and k17 (17, 19, 20,
21), place marker, work Seed st over next 22 sts, place
marker, work in St st over remaining 17 (17, 19, 20, 21) sts.
Shape Sleeve
Keeping continuity of sts in patterns as established, shape
sleeve by inc 1 st at beginning and end of every 2nd (3rd,
2nd, 2nd, 2nd ) row 3 (10, 4, 8, 12) times, then every 4th
row 5 (0, 6, 5, 4) times–72 (76, 80, 88, 96) sts. Work even
if necessary until piece measures 6¼ (7, 7½, 8¼, 9)” from
beginning, end by working a wrong side row. Cast on 60
(60, 62, 64, 66) sts at end of last row for Back –132 (136,
142, 152, 162) sts.

Does this mean that I just increase the St st, keeping the seed stitch the same number i.e 19 St st
Thank you for your help, I really want to do this

Welcome!
As i understand it, for the smallest size, for example, you have 17sts stockinette (knit on the RS, purl on the WS), then 22sts seed, then 17sts stockinette. All your increases are at the beginning and end of row so they’re all in the stockinette stitch sections. The seed stitch stays at 22sts throughout and is worked between the markers.
Can you give us the pattern name or a link?

Thats what I thought but I wanted to be sure. The pattern is Red heart cuff to cuff sweater LW2594 PDF
Thank you for your help