I see no one has answered; so I'll take a stab at your question. Other more expreienced growers can correct me an my ego will not be damaged. :)

I checked my 1976-2011 Composite guide book from ADS and my 2012 Classification guide book. Only Karma Lagoon is in the 2012 ADS book. It is classed as a 7309 (Waterlily = 73, Purple = 09)

The other two are not in either book. That means, either they were introduced before 1976 (not likely) or they have never been "introduced."

"Karma" dahlias are patented. That's a much different legal process than "introducing." A patented dahlia is not necessarily "introduced" by ADS; but it could be. Having a patented dahlia means is there are some hoops to go through if you want to hybridize them, and you CAN'T sell them without permission.

If a dahlia has never been introduced - that means they never scored in a trial garden, seedling bench, or won at least two blue ribbons in an ADS sponsored show during any one growing year. That does not necessarily mean it's not a good garden dahlia - it just hasn't been shown and/or it has not been successful at shows. Karma Lagoon has been sold a few years; and just now showed up in the guide book because it won a couple blue ribbons in 2011. It will stay in the guide book next year. It might also stay in 2013 - but only if it continues to win.

Why does anyone want to know the number? One (or two) reasons.

#1) You want to show the dahlia; and want to know what category it would be in.

#2) You just want to be able to better describe your dahlia; so that you know what size, form and color it will display.

If your answer is #1 - At the show, you will need to bring it to the judges; and they will "classifly" it for you based on how YOUR bloom looks. You can't just take the description of the seller.

If your answer is #2 - Check out the link I have below. It will help. You'll also need to know the difference between formal / informal decorative etc. And some of the color names are up for debate. But it's a starting point.

Take Fremont's Memory for example. Swan Island sells it and calls it a B ID Purple
B=2
ID = 1
Purple = 09

So Fremont's Memory is likely going to be in the ADS class 2109 as long as your's grows to the same size, form and color as Swan Island's. If you took it to a show, and it looked "pink" to the judges - they would put it in 2104 (04 = pink).

Anyway, that' a really long answer to your simple question. Hope it helps.

Here is a link that might be useful: ADS Classification