Theatrical costumes are not simply clothes for the actor - they have to indicate character, status or even emotion. These costumes for a Doctor and a Jew in the medieval Mystery Plays are doubly complex as they are not 'authentic' recreations of period costumes but recreations of how the Medieval world saw the past. The costumes have to indicate profession as understood by a general audience and so do not have to be academically accurate, but work in a theatrical context.
Although theatre designs are often considered works of art and are sought after by museums and private collectors, their artistic worth or decorative qualities are secondary to whether they 'work' on stage. The success of a costume design cannot be judged until it is translated into fabric, texture and decoration by the costume makers and seen as part of the whole stage picture. Some designers are very knowledgeable about costume making and produce very detailed designs, with notes on fabrics and making techniques, others create an 'atmospheric' drawing, which gives the feeling of the costume, and they then either work closely with the costume maker to realise their concept or have trusted makers who know their work and can create the effects they have in mind.