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North star / What counts as true

Only what was knowable at the time

Nothing borrows from the future.

We read every input as it stood at the moment it describes: which securities existed, how they were classified, what kind of market it was, and the data itself. Anything that could only have been known later stays out of the test.

That applies to labels as much as to prices. A market state decided by looking at what came next is a leak, however convenient it is.