I have a friend who found in an ATM the #ALG0000001 and after that, he got a replacement (AZA).
And this same friend found the radar 0001000 (or 0002000, I don't remember well), so this proves that the #0000000 is substituted by a single note replacement, not by a sheet replacement.
But in one instance, the #0000000 indeed found its way into circulation (a member in this forum reported this find made by someone else). To my knowledge, it's the only note #0000000 found in circulation, and not in the specimens sold by the BoC.
And I never heard about someone who got the first brick of a given prefix.