If a known exploitable vulnerability is discovered after placement on the market but before the final user receives the product, must the manufacturer re-open the placement decision?
No.
The Commission FAQ says the Article 13(1) obligation to deliver products without known exploitable vulnerabilities applies at the moment of placement on the market. Once the product has already been placed on the market, the manufacturer is not expected to fix newly discovered vulnerabilities before the product reaches the final user. But the manufacturer still has vulnerability-handling obligations during the support period and may need to provide a security update as soon as the product is put into operation by its user.
section 4.2.3
Article 13(1), Article 13(8)