Let’s try to clarify the issue and help the OP who probably started to be confused.
1). NaCl is a salt of a strong acid (HCl) and a strong base (NaOH). Furthermore, naphthalene sulfonic acids are strong acids, too. Consequently, there are (almost) only ions in their solutions; meaning that Na+ cations do not exclusively belong neither to chloride anions, nor to naphthalene sulfonate anions. All ions are in equilibria therein.
2). On the other hand, the concentrations ratio of acid salt and free acid depends on the pka and the pH only, regardless the presence of a buffer or not and where the cation comes from (common ion effect, among others).
3). But as mentioned above, Henderson-Hasselbach equation does not work well for concentrated solutions and strong acids. In these cases, more complex calculations are necessary.
4). However, the error of the Henderson-Hasselbach equation is considered negligible for dilute solutions of strong acids and their salts.
5). Besides and apart a few exceptions, the exact values for concentrated solutions of strong acids with their salts have poor practical value, as measures of comparison between acidic solutions.
6). Indicatively, an electrode pH-meter shows pH = -1 for a solution of NaCl in 6 N HCl; which is wrong (pH < 0 ) but everybody respects it, as being a comparison measure of how acidic this solution is.