The book cautions that not every form which looks exceptional by ordinary analogy is non-fasih. The decisive question is whether that particular form is attested in authoritative Arabic.
فَنَحْوُ آلٍ وَمَاءٍ وَأَبَى يَأْبَى وَعَوِرَ يَعْوَرُ فَصِيحٌ
Thus, forms such as “al,” “maʾ,” “aba yaʾba,” and “ʿawira yaʿwaru” are fasih.
Their present shapes may differ from an elementary expectation based on roots or general morphological patterns, but their authentic usage establishes their legitimacy. Attested forms cannot be rejected on the strength of a learner's oversimplified analogy.