لَيْسَ كُلُّ اسْمٍ دَلِيلًا عَلَى صَاحِبِ الرِّسَالَةِ.
Not every name is evidence of the letter's owner.
Laysa kullu denies the universal assertion: some names may not be sufficient evidence. It does not assert that no name could ever help identify an owner. By contrast, kullu ismin laysa bi-dalīlin is commonly read as denying evidentiary value of every name. Such changes of quantifier scope materially alter the claim.
A careful rhetorical reading therefore asks which universal claim is being denied and what possibility remains. Identifying a negative particle alone is not a sufficient account of the meaning.