There is another, Roman Chamomile, it is a perennial. There's a link below for more info(just the first one I came to in a search).
I grow the German and it reseeds every year...I actually haven't planted it since the first year...it just pops up everywhere LOL! If you cut the flowers off and don't pull up the whole plant, it will keep producing flowers until the end of the season. I just clip them off with scissors and let them dry in a colander.
It is certainly worth a try to sow some more seed now. Even if they don't flower before frost, you'll have volunteers in the spring from your first plants if you leave a few flowers on at the end of the season.

Here is a link that might be useful: Chamomile

1.How to grow chamomile

2.Wikipedia lists the chamomile varieties

3. Most dried plant stuff lasts roughly 1 year.

FataMorgana

I'm in zone 5. At this time of year, the chamomile that I have been picking on a regular basis is starting to fade badly. I simply remove the older plants and there are usually enough volunteers from self-sowing plants that I don't have to sow more seed (though you could if you wanted). I get another nice crop before the fall frosts.