There is that one lone article that Obama wrote around 1992 for a volume on Saul Alinsky - I think it was first published as a distinct article and then re-printed in the Alinsky volume. Cashill discusses it - he thinks it’s a clear example of Obama’s much more pedestrian and unimpressive style before he found any ghost-writers..... so using that article as a benchmark for Obama’s style (doubt that Obama had any ghost-writer for one article before 1993) could make the comparison possible.
No wonder his dissertations, papers, and everything have disappeared.
I guess it’s not enough if the “fingerprint” of Ayer’s writing matches the “fingerprint” of the ghost written work(s).