Two types of possible undergarment.
In the Lohengrin manuscript there are quite a few images depicting a woman sitting in bed with a white garment, a hemd or a nightshift (or are these of a similar type?). Only one of the images shows her with a sleeveless garment, which seems to have a waist seam attaching a gathered skirt part! This type is oftehn observed also in bathscens, the minatures below are dated from c.1400-1460s.
The second type of white garment, more commonly observed has a gathered area in the centre front with full sleeves, although not extremely wide ones. Is it possible this garment was also worn with just a sleeveless kirtle, for indoor/working conditions?
The big question is of course, is it really a hemd that we are seeing... What one can assume is that white gathered garment, showing through in the lacing gaps of bodice and sleeves, in this period was not sleeveless. It has atleast 3/4 lenght sleeves, possibly longer as the gathering and the elbow "steals" quite some lenght. Towards the end of the 1490s and the 1500s fully gathered/pleated around the neck opening can be observed, often decorated with some kind of pleatwork embroidery. For the early period it is harder to decipher the type of gathering, since the image sources in this period are not as detailed as during the following decades.
Similar garments can be seen in several variations in the many categories of art. In the Derich Baegert Cavalry scene Veronica wears one example, this one appears to have a pretty pleatwork embroidery around the neck opening.
There are also some Master ES engravings. The garment in the last image is not a hemd, but a sleeveless overdress. It does however show a very good closeup view of the small pleats/gathering in the centre front.