Why does a count “with tanwīn” require care?

Musāwāt and Ījāz al-Qaṣr: Proportionate Wording and the Rhetoric of Qiṣāṣ

• Because tanwīn always deletes a whole word
• Because it makes the verse conditional
• Because pronounced-letter counts may differ from modern written-character counts
• Because tanwīn belongs only to past-tense verbs