As far as I know, the Eida Hachareidis is not strict about this and does not insist on food under its supervision to be produced from flour ground after Pesach (correct me if I am wrong).
The notice says that some people are machmir on themselves to not purchase after Pesach chametz from flour that underwent a process of cleaning via a light stream of water before grinding.
The Eida says that some flour ground before pesach is ground dry, without undergoing that process using water. Such flour has the same exact status as flour ground after pesach.
I am not sure how helpful such a notice is. How is anybody supposed to know if a flour product is made from this flour or that flour, if ground before Pesach? Regardless, if there is a way to know, and if you are strict about this, the Eida says you can also eat from flour ground before Pesach if it was ground dry.
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