Cannot understand sleeve increases help!

This is what I’m making PatternI’m knitting sleeves in the round. The finished length is 12cm but It says to knit 4 cm rib then increase 2 sts every 6th row until the sleeve measures 7cm less than Finished measurements which is 12cm.

How is that possible? The ribbing is taking 4cm of the sleeve, plus the 7cm to reserve for diagram B. That leaves me with only 1cm to add 8 more sts!??

How can I do this? Do I have to increase within the disgram? You don’t normally do that.

What is written in the pattern:
Cast on and join (28) sts in colour 5575 on double pointed needles 21⁄2 mm and work(4)cm rib k1, p1.
Change to needles 31⁄2 mm and at the same time inc evenly spaced to (36) sts.
The first st is a marker st and is always purled. Inc 1 st on both sides of the marker st. Repeat inc approx every (6th) round to a total of (44) sts. NOTE: When the sleeve measures (7)cm less than finished length, work pattern according to diagram B.

It looks like a mistake in the number for overall length of the sleeve.

This chart gives the measurements for a yoked sweater which isn’t exactly the same as your pattern.

You could look for a comparable pattern with a drop sleeve and use the measurement for sleeve length from that or you could write to the company and ask about the pattern.