Well, to me it doesn't make much ense to worm them and not do the repeat, since there will presumably be a whole lot of unhatched eggs in there, if they have enough worms to need worming. Your math is correct. One thing you can do is worm them when they are molting since you won't be getting many (if any) eggs then, anyway. A lot of people only worm once a year. Heck, a lot of people don't worm at all -- but a chicken is going to get SOME worms, so many of us feel that at least once a year is good.
The first time I wormed, there was a decrease in how much feed they ate afterward, along with a bit of increase in their weight, or at least that's how it felt to me when I picked the few up who would allow me to. Naturally, I figure the worms were eating that much of their feed, before the chickens could digest it. I didn't see that dramatic a difference the next time, a year later, so I figure I'm OK doing it once a year. And I live not only in the type of area where there should be a lot of worms (warm and tends to be wet) but we actually had someone who worked for several days on his knees in the dirt get some worms under his skin, per his MD, so there's no doubt they are there.
Someone will probably question worming during a molt, pointing out that both are hard on them. I use Valbazen and my reasoning is, first, Valbazen is relatively easy on them as drugs go. Second, I wouldn't give it to a bird who was suffering with one of those awful, severe molts that turns them half naked and makes them obviously miserable. In my flock, you have to look closely at some of them to even be sure they are molting; fortunately, none get a really fast, severe molt. Of course, that means their molt takes longer, bur hopefully the tradeoff is they suffer with it less. Hopefully, also, you will give them a little extra nutritional attention, both for the molt and as recovery from the worming.
There are probably as many ways to worm as there are members here; this is just my approach and experience.
