re: They certainly checked in China
Yes, I should have added that the Chinese, not being influenced
by the goings-on in the less advanced cultures to their west,
and having called Sirius white from their careful observations,
only add to the idea that the Europeans just kept repeating
what was first said about Sirius being red - possibly due to its
being closer to the horizon back then.
Remember that the Chinese carefully recorded the supernova
that made the Crab Nebula in 1054 CE, but almost nothing of any
significance was said about it in Europe - and this SN could be
seen in the daytime!