From: DeathChicken | #021
I wouldn't say that, so much as they just kind of ignore it. There aren't any references in Peace Walker other than a character going "Let's try to leave all that behind us" in the beginning
More or less. I think there is one thing that happens at the end of PO that they reference in a side conversation, but otherwise the details of events in PO are ignored to the point where it makes more sense to consider them non-canon, whether that's true or not. PO itself still definitely happened, though.
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"One toot on this whistle will take you to a far away land."
-Toad, SMB3