I have no problem with Tilly deducing that there are at least ten generations of starships there.
What I do have a problem with:
1) Tilly seems to think this is a big deal. Her own Starfleet has existed for about a century; has there only been a single generation of starships in that time, to make ten per a thousand years seem impressive?
2) Tilly seems to devote considerable mental effort to arriving at this figure. As in, "I can calculate the properties of dark matter asteroids in my head, but how manieth letter of the alphabet was this J again...?"!
Timo Saloniemi
If it's actually 11 (as Owo corrected), it means they broke a cardinal rule of alpha-numeric listing and used a capital " I "
