When my flocks are on a layer ration and a female or so lays soft shelled eggs I assume there is a problem with that pullet/hen, since the rest are laying eggs with normal hard shells. Offering "free choice" calcium besides the breeder ration shouldn't be a problem if you want to do it. I generally don't do it, but I have in the past. I doubt they would consume too much.
When my young birds are maturing and on a growing ration I start adding calcium to the feed when I notice they first start to lay and then switch them to a layer ration the next time I order feed.
This past breeding season several pullets were in individual breeding coops and one pullet always laid a egg that was too soft shelled to set. I did add extra calcium to her feed cup, but it didn't help. Of course she was in the special breeding project because I wanted to produce more chickens with some of her extra nice characteristics, but due to the soft shelled eggs it just didn't happen.
I recall reading that some big commercial breeding flocks have feeders with layer ration at the normal level/elevation for the females to eat from and elevated feeders with a special male breeder ration for them.
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