A couple of questions.

I have a couple of questions regarding B-17 crews, aircraft, and markings. As a point of reference, the following questions arose after I found my Dad's crew photo on the 91stBG website. The A/C was "Gypsie" 44-8324 LL R. I know quite a bit about the aircraft and precious little of Dad's experiences.
 
How soon after a crew was assigned a specific tail number was their crew photo taken, generally speaking?
 
In the photo, there is a black painted arrow beneath the pilots side window, extending to the trailing edge of the forward stationary window. There are vertical bombs painted on this black arrow stripe, 38 of them actually. What do they represent? Also, below those and directly beneath the pilot's sliding window, at about the same level as the control access door are two more vertical bombs and what appears to be a partial bomb. I took these to represent missions, but I'm not sure.
 
Is there a database somewhere that would show where and when a particular aircraft was delivered for service?
 
There are gaps in the missions Dad went on, sometimes weeks, even a month or so, at other times they might be several days in a row. How was who flew when decided? Sometimes Dad or other members of his crew would show up on the load lists for other aircraft. Was this volunteered or by assignment?
 
Thanks for any help
 
Frank Drake  AKA sonofatailgunner