Proof game in 28.5.
16.5
The color scheme is daEggplnt!
This 16.5 is the (non-unique) SPG.
40.5, not unique.
Proof game in 26.5.
Is that unique?
No.
40.5, still not unique. Giving white a free move (Qg5-f5 here) is risky, increasing the chances of a dual.
Is there any way to make this idea unique?
A position with a lot of rooks.
Per the comp, it's unique right there.
However, the minute you move the Bishop from g8, you can promote either the R or the B first.
What is the idea? Maybe you should just stop at 25.0 moves.