Both serial traces were using the same microSD card only the original B was with an microSD-SD adapter therefore I'm confident that the image/SD are ok. It was created on a Kali machine using the DD command.

I have tried this with several different B+ devices and the results are consistent.

Searching on-line there are a few references about the change to lan9514 from the lan9512 chip for network and USB causing issues

The latest raspbian distribution boots and there are several references that if moving from a B to a B+ it must be updated before the move again referencing Ethernet and USB issues.

This might be limited to the display I have available but if the display is connected at power up there is no output. If it is connected after boot the display will show the Kali login prompt. (this only happens with Kali)
For some time before connecting a serial debug lead this caused me to think it wasn't booting at all.
In addition to the activity light characteristics are different, on the old model the activity light flickered during boot, on the new model it comes on for a moment at power up then seems to remain off.

Due to no Ethernet or USB there is no way to interact with the device for more information.