[jagaerglad]

Can't say much about the linked page but one could read the article[0] about the same topic on Encyclopedia Iranica, which is a better source since it's compiled and edited by scholars in history, linguistics, iranian studies etc. Haven't read them myself but they both mention the epigraphist Grotenfrend at least

[0]: https://www.iranicaonline.org/articles/epigraphy-i

[retrac]

The Cambridge Encyclopedia of the World's Ancient Languages: https://www.cambridge.org/ca/universitypress/subjects/langua... (available elsewhere for less...) also has a good chapter on Old Persian.

The chapter on Avestan is also relevant and interesting.