Part of this debate is arithmetic, true by construction. Part is genuinely contested. Separating the two makes the argument far easier to follow.
Half the Year Is Gone. How to Judge the Forecast You Made in January
Memory reorganises itself around outcomes automatically and invisibly. An unrecorded forecast cannot be graded, because what gets graded is a reconstruction.
‘Sell in May’: What the Seasonality Evidence Actually Supports
Unlike most market folklore this one has statistical support across many markets and long samples. It is still not usable, and the reasons illustrate a general problem.