Not quite on topic, but sorry, I had to:
Prusian is imho not eligible, there are no native speakers. There is little reason to believe that it is in a category similar to Ancient Greek.
For the rest it is fine.
For languages under revitalization efforts, if you look at example from revival of Hebrew, people start using Hebrew for daily conversation since year 1880s, and Tel Aviv established in 1909 as a Hebrew-speaking city, however it's only during Mandate period which start after WWI that people start teaching children with Hebrew as their mother language and thus to let them become a native speaker of the language
Nope, if you talk about when did people START it, then it's more like 1882:
It took a few years for more native speakers to be born. I need to check how many exactly, but I'm pretty sure it did not take forty years.
The first Hebrew kindergarten started in 1913 or so by David Yellin (accounts vary; and note that the whole concept of a kindergarten was only about 100 years old then).
The time of the British mandate (1920s) is the time of recognition of Hebrew as an official language, and the establishment of Hebrew higher education institutions. Thousands of those children had grown up and wanted to learn engineering and humanities somewhere. Publishing of (non-religious) Hebrew books and newspapers had been several decades old by that time.
Will this happen with Prussian? I don't know. I find Michael's attitude to this pretty balanced.