I am not a big fellow at 172cms and 66kgs and this is tight on me.
My guess is the original owner scored this as a gift but it just didn't fit them.
Labelled sizes are a real mine field so it's always best to lay
one of your own jackets flat and compare to the following.
Laid flat measurements:
Shoulder seam to seam 44cms
Sleeve length ( shoulder seam to cuff end ) 66cms
Under arm to hem 47cms
Waist 48cms
Shoulder to shoulder 44cms
Underarm to underarm 52cms
Call out if you want other measurements