I don't even know when the last merit source was added, but it was probably a long time ago
You are right, it was quite a long time ago indeed, as last time theymos readjusted merit was in June 2021.
and if it was recent it was probably to replace one or more sources that dropped out.
Effects of few merit sources leaving the forum are getting to be noticeable. As seen in the
Merit Dashboard, monthly merit numbers were usually between 24-27k ever since July 2021 and last month (February 2024), that number dropped down to ~20k, which is the lowest since that latest merit readjustment and if the number continues dropping, I think we might see theymos intervening again.