This doesn't appear to be universal then, because I've been told by Telcos in the UK and France that they will not block calls even when the presented number is impossible.

It was made clear that any call that was made to one of my numbers would be delivered irrespective of any faulty components visible to me in the SIP header.

Well this is certainly jurisdiction-dependent.

e.g. the CRTC has policy 2018-484, Implementation of universal network-level blocking of calls with blatantly illegitimate caller identification: https://crtc.gc.ca/eng/archive/2018/2018-484.htm

CRTC gave telcos twelve months to implement, and it seems to have largely been implemented within that time frame.