Although I don't know of any books on the issue off the top of my head. I can give you some very sound advice on buying a Browning A5. First of all, its good that you are accessing info on the serial numbers, this is a good thing. Second of all ( and probally most important ) is to look for ANY alterations that have been made on the gun. With a Browning A5, original condition will be the key to its value. I have seen alot of A5's at gun shows that have been altered and the dealers selling them are asking prices that should be put on fully original guns. Because an A5 thats 100% original in excellent condition will command a high price, ALOT of people end up buying an A5 for a high price, and get ripped off. Most people feel that its worth money just because its an A5. The most common things I see being altered on the A5 are as follows.
Barrel length- be sure its the right length for the gun. Alot of these barrels have been cut down and usually measure ( open choke ) when the barrel is marked mod/ improved. If the barrel is marked mod or improved, and you measure the choke and its reading open choke, then odds are, it probally has been cut down.
Refinished stocks, alot of people will refinish the wood in order to enhance the appearence. This makes the gun look good, but decreases it value.
Shortened stock- Back in the hay day, they didn't offer " youth guns " like they do today. Alot of A5's stocks have been shortened to accomidate the length of pull for younger hunters, women, or smaller men. Again this decreases the value.
A rebluing job - Of coarse, there are a TON of A5's out there right now that have been fully refinished and reblued to enhance its appearence and to FOOL the uneducated buyer. Look for shallow pits that might have been covered up by a reblue. This is evidence that the gun was once rusted and the restorer didn't file deep enough to get out all the pits. Look for shallow lettering and serial numbers that are worn down. If they are shallow and worn down to almost non existant, then so should the bluing around it. If its a perfect blue over the shallow lettering and serial numbers, then you know its been reblued. Look for period correctness in the color. Modern bluing jobs will be different in color than the bluing jobs of old. A good way to determine modern bluing is to go to a gun store selling new firearms. Pic up a new Browning BPS. Look down the barrel, hold it at an angle, and turn it slowly back and forth. As the light hits different angles, you will see colors that immitate colors in an " oil slick " blues and purple tones in an otherwise black looking barrel. These purples where never present in the old blues of a Browning A5. Most original blue jobs will look black, with greyish " coal like tints" That appear range from blue to a graphite color on tour pencil lead. A more " dull " look than a very Radiant bluing like alot of modern blues.
recievers tapped for scopes or reciever sights- Look for recievers that have been tapped for scopes or for extra holes or screws filling in those holes on the sides or the top of the tang on the receiver.
Poly chokes/ celect a chokes. These are ugly looking at the end of a barrel. Dont get burnt buying one of these, if you want an original.
An A5 made in portugal or Japan. - Check the stamp on the barrel, these are less sought after than those stamped St. Louis or belgium. If you buy one, make sure you are paying alot less than the ones stamped St Louis or Belgium.
Swing swivels- Look for swing swivels installed into the butt stock. I wouldn't want to pay good money for an A5 that has holes burrowed into the stock.
These are just some of the things to look for, I hope I helped and didn't ramble on too much. Just a word of warning, most A5's that are exceptional condition are rare. Any that you find, you should be speculative about and use caution before forking over any big bucks for it. God bless and good luck searching.