وَالْمُطَلَّقَاتُ يَتَرَبَّصْنَ بِأَنْفُسِهِنَّ ثَلَاثَةَ قُرُوءٍ
Divorced women shall wait concerning themselves for three qurūʾ. (Qur'an 2:228)
The word thalāthah (three) denotes a fixed number. As a numerical expression it is specific: two or four cannot simply be substituted without evidence.
The exactness of the number and the interpretation of “qurūʾ” are distinct questions. A fixed numerical expression does not automatically remove every ambiguity from all neighboring terms.