Does the highlighted part of the text below mean "but the artists chose style, the number of artworks, and subject matter"?
Context:
As with the First World War programme, artists employed a variety of styles, from traditional to more modern. Their contracts or commissions required them to produce specific types of works – canvases or works on paper, for example – but they chose style, quantity, and subject matter. They included many high-profile artists, but abstract painting did not fit into the programme, thus excluding even Ben Nicholson.
The lead-in to the section you have highlighted is a bit awkward and "they" is referring to the organizers.
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