A few hammer gun questions

[Phil C]

Took a look at a couple of Parkers today. S/N 34172 a 12 gauge 2 barrel set with individual forend for each barrel, 30" and a 25 1/2 sets and serial numbers all match.. I am guessing that the short set has been cut but it appears to have a keel. Looked up the S/N in my Parker Gun ID and S/N book and it is not listed. Look on the web site and it states there are surviving records. If there are surviving records why was this not listed in the book? I am sure I have heard the answer in the past but just do not remember. Also what is the chance barrels would be listed in the records? Gun was made in 1883 on a one frame. How common would a 2 barrel set be during this time frame.
The other gun is S/N B 1543. No records on this gun, but I do not recall why some guns were marked with the B. Damascus barrels, straight grip lifter. Bores a little rough and loose on face. Not bad for a 140 year old gun I guess.