Had no idea about the D3 building up. Good to know!Calcium citrate with D3 is good to use for the purpose of treating a hen with immediate reproductive issues, although it's fine to use the plain. The length of time such a hen is going to be on calcium is of a short duration, usually no more than three to five days, no harm that vitamin D is going to build up in the fatty tissues to a toxic level in such a short time.
For the purpose we are using calcium citrate, to help a hen expel a stuck egg or broken egg material, D3 is very helpful in getting the calcium absorbed quickly and efficiently. Do not worry about D3 building up to toxic levels using it in this manner.
On the other hand, I sometimes need to treat a hen for poor egg shell quality. For this purpose, I use calcium citrate without the D3 since she may be on the calcium as long as a month. I had a hen at the beginning of spring that was having a heck of a hard time with two eggs in a 25 hour cycle, and her shell quality was paper thin. She had to be on calcium for two months. It did the trick. She began laying normally and the shell quality is now very good.