I don't know how to ID the age. the serial number (typically molded into rim where you'd glue the tire, on a white rectangular piece of paper) can be cross referenced by Zipp and ID'ed.
When I was big into the 340's and 440's (i.e. the first few years they made them), there were something like 10 or 15 internal updates made in one year (!).
My experience with them is that you must not tension them too much (they have a tension number they recommend but I don't have that info anymore). If you tension them too much, the rim halves (they are clamshell like) will split and let the spoke nipple through. When I say "not too much tension", I mean so little tension that it seems like the wheel was just laced. Threadlock of some type was critical in keeping together a set of these wheels.
The newer wheels have significantly more tension from the factory so they must have solved the "split" problem.
Having said that, if the 440 has 24 holes, it'll make for a great front rim (not too much tension required). More spokes and a lot of the aero benefits are negated. Rears are possible, my experience is that they worked best with 32 hole hubs - 16 right spokes (x2), 8 lefts (radial). This way the lack of tension won't weaken the wheel too much.
They are very aero and very fast. They accelerate a little slower than "light" rims (340's and similar weight rims). They annihilate brake pads, esp in the rain (they have a textured braking surface). They make a lot of noise when braking.
I also have a 440 and am probably going to build it into a spare front wheel (24H). It is currently laced evenly on a 24H rear hub and is not very usable.
On weight, the name of the rim reflected the weight. With the updates, I believe the 440's were slightly under 440 grams (420 or so). I don't know about the 404's but I imagine they are 400-ish grams. This is remarkable since many rim weights are very optimistic.
hope this helps
cdr
