I've noticed a sub-trope of this where a character in a flashback (usually set in the 1970s or 1980s) had a mustache. An example of this is Dan Conner in the Rosanne episode "Second Time Around" during a flashback to DJ's birth. Another example is the Venture Brothers episode "Powerless in the Face of Death" where both Dr. Venture and Brock Samson had mustaches in a flashback.
I've noticed a sub-trope of this where a character in a flashback (usually set in the 1970s or 1980s) had a mustache. An example of this is Dan Conner in the Rosanne episode "Second Time Around" during a flashback to DJ's birth. Another example is the Venture Brothers episode "Powerless in the Face of Death" where both Dr. Venture and Brock Samson had mustaches in a flashback.
I call this trope "Past-stache."