The Cornides report predates the widespread news of killing at the Reinhard camps which only began to widely circulate towards the end of 42.
As for using "unsubstantiated hearsay" we can for comparison purposes examine some of the revisionist witness evidence for resettlement as shown in the Kues series
https://codoh.com/library/series/eviden ... -the-1/en/As you can see, he mostly uses Jewish sources (people confined or held prisoner by the Germans) and none of these sources directly or indirectly state resettlement happening, rather just property of Jews arriving in the East, or reporting on (unsourced, unsubstantiated) rumors of Jews being killed. Kues does not provide any witness testimony (whether sourced or unsourced) of Jews being resettled.
Basically what makes the Cornides report convincing (if taken at face value) is that the sources he uses are Germans living and working near the camp. These were people who could freely move about, ask questions, make observations, as opposed to the Jewish sources Kues uses in 3 part series. The most damning part of the report, and one no one here has addressed, is that it would have been just as evident to people that Jews were entering as leaving. And if Jews were leaving Belzec en masse, then no mass killing. But Cornides doesn't report on this, which is why I posited that within the revisionist framework, it would seem that not only were local Germans spreading wild and horrendous rumors about their own people, but they were also actively lying to Cornides about not seeing massive transports leaving the camp.