They also excluded studies where people took supplements that included vitamin D. Not sure about New Zealand, but pretty much all supplements in the US include both calcium and D. However if you just take Tums, that does not have Vitamin D, IIRC.

Also from what I've read, the calcium gets absorbed better if you don't have too much at once, so for that reason also it's better to spread out the supplements over the course of the day instead of taking them all at once. I take a multivitamin at breakfast, which has some calcium in it, so if I take a supplement I take it with lunch. But my bones are ridiculously dense already and I eat lots of dairy products, so I don't take the supplment every day and at most I only take 1 per day (600 mg calcium).