EBU Single Rulebook Q&A 7 March 2019 2019_4598 Use of rating before or after transfer in the calculation of the one-year default rates

In a situation where a parent institution (good rating) has issued a full encompassing guarantee for a subsidiary - bad rating, thus supporting the subsidiary before a default event, and preventing (or reducing the risk of) a default – would this constitute a substitution effect due to a credit risk mitigation under paragraph 74 of EBA Guidelines EBA/GL/2017/16?