Yamaha models include the letters YAS which in this case means Yamaha Alto Sax. Some other models are:

YSS - soprano sax
YAS - alto sax
YTS - tenor sax
YBS - baritone (bari) sax

Yamaha's numbering is based on the following system:

2 = Beginner
3-5 = Intermediate
6 = Pro
8 = Custom. The z and ex models are extensions to the 8 series.

I know of no site that will provide you the date of a Yamaha by the serial number. You might be able to find out the production date by contacting :

Yamaha Corporation of America
Band & Orchestra Division
Wind Instruments
6600 Orangethorpe Ave
Buena Park, CA
90620
(714) 522-9011
Internet: www.yamaha.com/band

Ask to speak to the customer support and they can help you. In an earlier thread, someone bought a YSS-875 and called them first to run the serial number and they were able to give me the day that they shipped it to the store; and they told him that usually it is finished the same week that they ship it. This doesn't give you the date of manufactor but will get you pretty close to the date (plus or minus a year).

Virtual tour of the Yamaha factory http://www.yamaha.co.jp/edu/english/factory/sax/
http://69.28.71.25/gsfactour.WMV Yamaha factory tour video. Bad jokes, cheesy music, but kinda interesting for sax players none the less.
More at http://www.giles.com/yamaha1/PR/MUS/bno/index.html ???
Their press releases might have more.

Yamaha Line Parts Lists:
http://parts-search.yamaha.co.jp/html/WIND_ENGLISH/orders/group_e.php

They have 11 product lines:

* 1 Q Series (YAS-01)
* 2 23
* 3 ADVANTAGE 200
* 4 275
* 5 475
* 6 ALLEGRO 575
* 7 YBS-32E and YBS-52
* 8 62
* 9 675
* 10 82Z
* 11 875

The 23/25/200 are essentially the same horn; we're just talking an altissimo F#, lacquer color and the name stamped on the bell.
The 475 = 32 = 52, so that's really the same family. For the sake of argument, let's throw in the 675 with the 62's.