I think Data can
actually use contractions. He just doesn't want to. He even does occasionally.
I remember one of his very first lines in "Encounter at Farpoint" had a contraction.
In "Genesis" if you listen close enough, Data said "She's no longer human." (When he and Picard discover the Amphibian Troi).
I even remember in "Datalore" when Tasha and the others check on him after he and Wes managed to get Lore out of the cargobay, he CLEARLY said "I'm fine."
I remember I kept watching that again, trying to listen for "I am fine" but he definately said "I'm".
So, what's with Data and not using contractions when even Lore in "Data
lore" used contractions.