en.wikipedia.org/wiki/Pope_Innocent_III

Primary and reference sources contradict both parts of this sentence.

First, Innocent III did know of the diversion before Constantinople was sacked. A contemporary source preserving Innocent's warning to the crusade leaders quotes him telling them that, even if the Byzantine emperor had done wrong, "it is still not your business to judge their crimes" and ordering them not to attack Greek lands. That warning is tied to June 1203, well before the April 1204 sack.

Second, Alexios IV was not crowned only after the city had been plundered. Standard emperor lists place Isaac II restored with Alexius IV in 1203–1204, and then note the loss of Constantinople in 1204. So Alexios IV's restoration/coronation belongs to 1203, months before the 1204 sack.

So the article sentence collapses two different events into one: Innocent already knew of the Constantinople diversion before the sack, and Alexios IV's elevation happened in 1203, not only after the city was plundered in 1204.

This sentence misstates Baldwin I's title. Reliable reference works identify Baldwin I as the first Latin emperor of Constantinople, not the "king" of the Latin Empire.

Britannica states that Baldwin I "became the first Latin emperor of Constantinople". The British Museum likewise identifies him as "emperor of the Latin Empire of Constantinople." Because the Latin Empire's ruler held the imperial title, calling Baldwin "king" here is incorrect.

The figure 20,000 is widely associated with the Massacre at Béziers in July 1209, not with the entire Albigensian Crusade.

Britannica's entry on Béziers says that 20,000 residents were killed there in that single massacre. But Britannica's entries on the wider Albigensian conflict describe a war running from 1209 to 1229 and refer to "wholesale massacres" during the war. That means the article is taking a number tied to one early episode and presenting it as if it were the total death toll of the entire crusade.

A precise overall casualty total is difficult to establish, so the safest correction is not to replace it with another exact number, but to note that ~20,000 is not a credible total for the whole crusade because one of its first major massacres is itself commonly given as 20,000.