Why not do the same as I have with my folder structure?
{author_sort:switch(^[A-D],[A - D],^[E-J],[E - J],^[K-O],[K - O],^[P-T],[P - T],^[U-Z],[U - Z],[Other])}
So, something like:
{series_index:switch(00[0-9][0-9], 0000-0099, 01[0-9][0-9], 0100-199, ....} etc...
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