Yes, it does happen from time to time...a G-AIRMET somehow gets issued that just doesn't make sense. Imagine for a moment that you are flying out of central Michigan at about 0000 UTC. So prior to your departure, you call Flight Services to get a standard briefing. You tell the briefer that your plan is to fly IFR at 7,000 feet and you are not equipped with a certified ice protection system (IPS). The briefer tells you about an AIRMET for moderate airframe ice from 4,000 to 10,000 feet covering most of lower Michigan. The briefer says that he would not recommend an IFR flight at 7,000 feet given the risk of moderate airframe ice along your proposed route. You hang up the phone with the understanding that you are not going to make this flight.
So you get online and start to examine the weather more carefully and you notice the legacy AIRMET the briefer was telling you about.
WAUS43 KKCI 092048 AAA
CHIZ WA 092048 AMD
AIRMET ZULU UPDT 5 FOR ICE AND FRZLVL VALID UNTIL 100300
...SEE SIGMET VICTOR SERIES...UPDT
AIRMET ICE...WI LM MI LH IL IN
FROM 20NNE GRB TO YVV TO 20ESE DXO TO 20WSW GIJ TO 20SW ORD TO
MOD ICE BTN 040 AND 120. CONDS CONTG BYD 03Z ENDG 06-09Z.
Here's the G-AIRMET snapshot valid at 0000 UTC...