Sometimes he wrote a rough sketch on the lower part of next page that was separated by a continuous line from the rest of the manuscript. As this sketch was worked out, he transferred its contents to the upper part of the page.
This approach was not unusual for the eighteenth century and various versions of it survived into the twentieth century. Thus, I was taught (late fifties, early sixties) to divide every page in a notebook in half by folding it (and then flatten it again). The first draft was to be written on one the right half of the page. The other half was to be used for revisions. What makes Hölderlin's approach remarkable is that he planned for three times the revisions (and apparently used up the space as well). Among other things, this shows that his poetry was not the result of sudden inspiration, but of gradual reworking of the first draft. The editors of the Frankfurt Edition of Hölderlin's work like to speak of "ideal growth."
Whether "ideal" or not, this kind of growth is difficult to see in an electronic text, unless, of course, the author used version control. This may not be a bad thing entirely