Background to the hockey stick issue:
Warmists use a unique and non standard method for combining temperature proxies, such that if one combines a hundred supposed proxies, one of which, due to luck, cherry picking, or random error, shows a hockey stick, the entire graph of the supposedly combined proxies will be dominated by the one that shows a hockey stick, and not the ninety nine that do not. Thus the history of the hockey stick is the history of discovering smelly data among those supposed proxies, and demonstrating that the supposedly combined graph is fragile, in that when a small handful dubious cherry picked outlying items are removed, the entire graph radically changes shape.
The decline that had to be hidden in “hide the decline” was that the curve was pieced together out of random noise proxies, and thus they used one temperature indicator for one period, and a different temperature indicator for another period, patching together the story that they wanted the data tell from indicators that told different and contradictory stories, as if making a ransom note out of words and letters cut from a newspaper. What was hidden was that one supposed temperature indicator failed to agree with another.