effect Reveal_Cities - when a city is no more
That's also used for civ1 Apollo Program (and has existed for that use for a very long time). Not sure if we should research civ1 compatibility point-of-view, or would we consider this a bug in civ1 even if the not-disappearing behavior is there (we are not supposed to be bug-compatible)
3.0.0
civ2civ3 and sandbox rulesets have wonder "Internet", with effect "Reveal_Cities". While in effect, when there's a new city it appears to the wonder owner, but when a city ceases to exist it doesn't disappear. Not hard to repro using editing mode.