Your patter is vintage. Back then Waistcoat had a band collar of upper fabric that run across the back neck and covered a bit of the shirt collar. The strip had a finished width of about 1,5cm. This strip is never mentioned in the Rundshcau patterns, probably because it was coonsidered as a well known fact. But the pattern mentions the transition area between the front edge and this band collar, wich is the 1,5cm from H1 to h1.
So H1 and H go together and A2 and a2 go together. The back shoulder will be 1cm longer than the front, wich you have to ease in. This 1cm is a kind of dart for the shoulder blades. (When you have a back shoulder that is longer then the front your armhole will gape like in your toile).
When you don´t want a back collar stand just skip the 1,5cm from H1 to h1 and let the front edge end in H1.
When you want to add the band collar( wich I consider the "Taylor´s choice") you have to attach a strip of cloth as a back collar. it´s finished width is 1,5cm, it´s finished Length is the same as W to H.
There are some threads about this waistcoat detail, so have a look.