This is a fundamental breach of the prosecutor's duty to disclose any evidence that undermines the prosecution case or supports the defence case. This duty continues to exist after conviction so timing of knowledge is irrelevant.
The judgment is telling in that there are records in which Post Office officials made statements that minutes of meetings about faults in the Horizon system should not be taken so as to avoid having to disclose them in proceedings.
It is corporate failure on an unimaginable scale and three convicted individuals have died before having their convictions quashed.
Yesterday's judgment is long but very readable. I would anticipate further fallout and understand there may be a live police investigation on the basis that several individuals may have perverted the course of justice by either proceeding with prosecutions or omitting material evidence from testimony.