I have merged your question into the existing discussion. As far as I know it's still 24 months from the last Sapphire bonus, not 24 months from account closure.
Here are the terms of a current Sapphire Preferred offer:
Looks like the term has not been changed and the agent I spoke to misunderstood the rule. DP: 1st CSP applied on 11/16/15, got bonus on 12/16/15, downgraded to CFU in 10/2017 and was approved for 2nd CSP on 12/17/17.