First look at the panel approval. I have seen panels approved for 24 circuits with 32 circuits coming out because the electrician installed 16 tandem breakers or some combination of full sized and tandems to exceed the approved number of branch circuits. IE a 24 circuit panel with 12 tandem breakers is full even if there are 12 spare positions left.
So in order for a brand new house to meet code there could be 10 tandems installed into a 24 circuit panel leaving 2 spare positions that may be used and a bunch that would create a violation.
Most modern panels are simpler in that if there were 24 possible full sized breaker positions the panel would also be approved for 48 1/2 sized breakers too.