Yes, but the two links that I checked from https://blog.aerohive.com/author/davidcoleman/ wind
up on a generic ExtremeNetworks page.
However, the Wayback Machine is your friend:
You're right. Sorry for not checking the actual links and thanks for
finding the articles on the Archive.
The material is the blogs is in the CWNA 5th Edition Study Guide.
Note, however, that the OFDMA DL explanations don't really explain
what products (at least those that have enabled OFDMA) are doing.