Let's see - Steel Shadows/Wells steps in behind the scenes with a future version of 'Bummer Be Gone'
Zara and Ching (being telepathic and all) zap everybody with a version of the 'forget kiss' from SII.
The whole town stays quite about it except for the couple of people who tell Spooky Mulder and since nobody believes him...
A secret government agency swears everyone to secrecy.
Martha and Jonathan, Lois and Clark convince everybody that Nor was completely delusional and was liar's blackmail on Clark to get to Superman.
I'm sure there are others.