1820 - Rome captures Khabarovsk from Russians.
1831 - Rome gets the Better Coal Fuel event, all current Roman cities
(including Khabarovsk) get the drydock production & health bonus
1832 - Rome captures Yaroslavl from Russians; as this came after the event
it only gets the drydock health bonus.
.... - As with Yaroslavl, all other captured cities in this time-frame are
missing the production bonus.
1978 - Rome captures Nicomedia from Aztecs; this is the last coastal capture
without the drydock production bonus.
1980 - (July) Aztecs get the Better Coal Fuel event and also pick the drydock
option; all current Aztec cities (including, for example, Larsa) get
the drydock production & health bonus
1986 - Rome captures Larsa from Aztecs. Because this city had the drydock
production bonus from the Aztecs, it retains it after capture.
.... - Future cities captured from the Aztecs retain the production bonus too.