The originals of the 17th century were not painted on canvas like the thangkas. They were based on rectangular pages of stiff paper like those usually used for Tibetan sutra texts.
Two or three pages in portrait or landscape format were used for one image. When put together, the result was the overall image of a picture. The above graphic illustrates the compositions
Our copies were painted on canvases that are usually used for thangkas. You can tell on them only by the formats whether their original was portrait or landscape and whether it was two or three pages.