I agree with Bez as well... The numbers are a good guide, but not the law. I also work hard on having cows that can deliver anything that can be thrown at them... About 4 years ago, the average BW of the herd jumped by about 15 lbs and stayed that way.. have no idea why as the bull was the same as before, and even with the following bull the BW's stayed up. I visited a neighbour across the river from us and was shocked to see these tiny little calves after having gotten used to ours. The birthweights on my bull calves this year has been 90, 100, 2x 110, and 2x 130, my second calvers both had heifers calves at 80 and 90 lbs, and despite checking on them regularly I haven't caught one of them in the act yet. So while the numbers we have may scare some people I see no reason for it.
I also think that BW is only a small part of the calving equation... We've always selected bulls with no protruding eyebrows, narrow heads, long bodies and long noses. It's pretty simple to see that a 100 lb calf shaped like a wet noodle will not be an issue, but a shorter one of the same weight has to be wider, which is the problem.
Good to hear that at least 3 of 4 of your heifers have done well