Hi, Jo,
(You ask for comments, you get 'em!)
I don't know the authoritative response, but I *think* I've read of births occurring as short as 8.5 months after the last delivery (implying mating a month after birth). I can't remember where I read that (maybe I should be assembling a library of info). As with anything, I would think it would depend on the health and condition of the mother.
I *do* know that mating does not necessarily equal pregnancy. I've observed actual copulation, with a birth occurring *9* months later. If gestation = 7.5 months, then the copulation I observed was NOT the one that resulted in the subsequent birth (either that, or the females store sperm, which is not unheard of in other reptile species but which I have no basis for assuming yet in Corucia).
Generally, mine get "frisky" whenever we get a good rain around here (I'm in Southern California, so we sometimes go months between rains, so I've noticed the correlation) -- despite the fact that I keep drippers and vaporizers going in the skink room almost full time, they still seem to tune-in to that outside rainfall somehow. I have observed mating behavior in February, April, July, and December. Thus far, I've had three babies born: one in 11/05, one in 11/06, and one in 12/06. But I also have another female who looks very pregnant right now... Go figure! Sometimes I think they just _enjoy_ courting and/or mating! It may be, as well, that something (such as a humidity spike from rainfall) triggers courtship and mating behavior in the *males*, whether or not the females are actually receptive at that time.
I would think that your observed courting/mating behavior implies your animals are healthy and frisky, which is probably a good sign. She might not become pregnant from a mating at this time. But if she *does*, I think that's not unheard of. How is the mother's weight? Does she look fat and healthy? If so, I wouldn't worry too much. (I would only worry if she looked underweight or weak).
Also, do you know if the twins she gave birth to were her first pregnancy? I had one deliver a slug a year and a half ago, and I think it was because it was her first pregnancy and she may have just been too young. I am guessing that potential problems might be more likely with a first pregnancy and/or young mother, and that subsequent pregnancies would be more likely to go smoothly. (Just a theory). Back when I used to breed snakes, I occasionally saw small clutches and miscarriages ("slugs") from first time mothers that didn't happen with subsequent pregnancies.
I hope that helps put your mind more at ease. Be aware, too, that some females seem to be on an every-other-year schedule for giving birth. (It could be that that has something to do with their ages -- I just don't know yet).
Sherri or Brian could almost certainly weigh-in with a more authoritative answer.
-- Celeste