I wonder if there is something wrong with my conditions.
I have over 50 splendiana x veitchii x tiveyi seedlings that I got from the
same person you did. However it's been over two years, and the seedlings are only about the size of a dime or quarter in diameter. None of them have died, but none are as large as yours
My growing conditions are fairly cool.
Summer 75-80F days with 58-65 F Nights
Winter 60-65F days with 50 F nights
Is that why they're still so small?