Likely none, as 5e wasn't released under the OGL originally. That didn't happen until early 2016 (at the same time as the DM's Guild launched), so a little over a year after the initial release.I wonder how much of that immediate resurrection was due to the less-restrictive OGL, and the influence of third-party publishers?
As I recall, they did speak about it before that, saying essentially that they were going to publish an SRD but needed some time to figure out exactly how much to open it up.