Intermittent problems that turn on the MIL (malfunction indicator light) or CEL (Check Engine Light) will allow the light to turn off after awhile. The code(s) are still in the ECU so you can read them.
One exception is the code for one (of two) malfunctioning knock sensor..it didn't set a CEL or flashing CEL on my 2K4.2 but the car ran limp/little power. Sometimes it would pick right up and run normally, other times it wouldn't run right until the engine was shut off and restarted. VAG-COM caught the bad knock sensor only when it happened while the car was not running right.
In your case the codes should be stored and accessible via OBDII system reader or a VAG-COM.