Amar, I did not know you had low C and Bb whistles! 
When did you get them?
Since a few makers have toyed around with extra high As, it could be argued that there are three As. A above Generation high G, A below Generation Bb, and A below low D, C, and Bb.
Steven, i got an alba combo lowC/lowBb, got it beginning of this year. 
Cool. No problems with the spread on the Bb?
I was playing two part duets with Renee out of our hymn book last night, her on high D and me on a low A to get those below D notes. Too close in tone and volume. I know what Wombat means about the “low A” being questionable as a low whistle. I am now thinking I NEED a bass A to really make that type of playing sound nice!!! Oh Mr. Goldie!!! 
i really reach my limits on the lowBb, can’t really manage it that well, i must try using the piper’s grip for my upper left hand too, that transition i somehow for some reason never could make.
I’m impressed by the range some of you have - the only keys I have below a Gen Bb are A (alto), F (alto), and D (tenor)
I’d like to add a G, and perhaps another each (different makers, for different moods) in A, F, and D. Maybe a C as well. Dunno about an Eb. Really skeptical about being able to play a low Bb.
from top to bottom;
Bb - a couple
A
G - had several, still got one but am still looking for the “right” one
F - a couple
E
D - several
I’m also working up to ordering a low C sometime soon. I find it’s fun trying the same tune in multiple keys. Also, some days, I just feel like playing a higher or lower sound.