Late lambs

Hi, back in early July I bought 8 dorper ewes from a guy that was selling off his flock. He had a total of 50 ewes and had placed the ram in with the flock march 15. With that date of introduction the lambs should have come in late august through late September. So far I've had one ewe lamb on august 23 and the other 7 ewes have not even dropped bags yet. They appear to be bred but no signs of lambs coming soon? He did not use a crayon on the ram but they were together up until July when I bought them. Does it sound like there may be a problem with the ewes or is it normal for it to take a while to get bred. If I have calculated correctly if these 7 were to all lamb today that means they would have been with him 7 weeks before being bred. And with no bags yet I highly doubt the lambs will come soon.

I'm not familiar with Dorpers, but some sheep are seasonal breeders and are unlikely to come into heat during the summer.

Edited to add: Ok, I looked up Dorpers and it appears they aren't seasonal breeders. I found this on Sheep 201: "single-sire matings run the risk of low conception rates or an extended lambing season if a ram with reduced fertility or libido is used". Maybe 50 ewes was a bit much for that ram, and it took awhile to get them all bred (if they are)? Other things can affect a ram's fertility too, for instance if it was really hot.

The question is "is the ram a dorper?" I have dorpers and they really are year round breeders, easily breeding back 3 months after lambing, any time, reagrdless of heat or time of year. They also tend to lamb at about 142 days. Bag development can be a bit variable, as I am sure you've heard, but the lack of lambs at this point make me suspicious of the ram's breed and quality.

What about the ewe's? If they're over weight, it takes longer for them to "take". I help an old sheep farmer that took one to market in the spring that has always been "huge" and has never lambed in 3 yrs, she was covered each year and a marked butt. Had a fertility test done and came back good - she was just to 'Fat".