I feel certain that gun has been around for some time. Here's the GI link:
https://www.gunsinternational.com/gu...n_id=101038310
The Parker letter in the ad actually references 2 guns. Serial # 158188 which appears to be the # on the trigger tang and is in the book as an AA. Then it references Serial # 145198 which is a DH 20 and it appears to me this is the # on the water table but I cannot say for sure, poor pic. Maybe someone else can see that number more clearly. Why would the letter reference 2 guns ??