What Properties Might Light of Millennia Past Have that Today's Doesn't?

The issue of bang is highly relevant so there is no digression. If the concept of bang is accepted at face value then the bang is the ultimate source of all light in the single common for all the existence past. A single location for the origin of light. No way to compare and verify its properties therefore we are forever in the dark unable to answer the question in the OP. Whereas what I was proposing in accordance with relativity of simultaneity was that light comes here from multiple pasts and countless locations and directions and the properties of light coming from one location can be easily verified by and compared to the same properties of radiation signals arriving from all other directions and locations in the cosmos.Edited by Alfred Maddenstein, : No reason given.Edited by Alfred Maddenstein, : No reason given.

No, so called CMB radiation would be no exception. When I say light I do not mean only the visible range of radiation signals. I mean any radiation. So that radiation of that wavelength would be coming from different pasts and locations just like any other. The Earth is then its source too.