In most gharana usage Ta and Na name the same stroke: index fingertip to the kinar, neighboring fingers damping at the syahi's border, quick release. Which syllable is spoken depends on context and school — thekas conventionally write Ta through the khali section, where the bayan drops out (Dha minus Ge leaves just the edge tone).
Some lineages do keep a separate, more closed Ta at the rim. When a notation seems to demand two different sounds, the teacher's nikas is the authority; the syllables are labels, not acoustics.