To know if it is truly Cryptocoryne Spiralis you would need to see it fully grown in the seller's / purchaser's tank because a lot of sellers of Cryptocoryne Spiralis sell Cryptocoryne Albida which is not the same no matter how much they say it is (including some German sellers that are extremely reputable)
The Cryptocoryne retrospiralis that Aquatic Magic used to sell was actually normal Spiralis. I had some of that. Grew exactly as Richard says. Some was 60cm. I sold it off ages ago foolishly and have tried to buy some more each time being disappointed.
I have just purchased some of this though as I trust Richard
there are different forms; some have numbers after them, you know like the H.siamensis 53b that you sell. I think one is named "Shola".... I am not sure why; Shola forests are unique highland forests in the W.Ghats in south India.
My understanding is that there are different forms of the plant, possibly natural, some might be cultivated. I just wondered whether your supplier knew which it is, or maybe they do not.