Spring cabbages are usually sown in July and August being planted out in September and October to slowly grow over the winter and be harvested *from late February through to the beginning of June*.
http://www.allotment-garden.org/vegetable/cabbage-types.php

The link I gave below for the Thompson and Morgan seed company (in the UK), which sells seed for "Derby Day" (one of the cultivars you mentioned) calls it summer cabbage. There are indeed many differences between UK and US English in agriculture. In fact the second (US) site I gave you uses the term early cabbage, as Alice has already suggested.