Bruce wrote:

Introducing an earth tail when not required does introduce
additional failure modes.

Such as?

By always fitting an earth tail, I think the benefits to the integrity of
the earthing scheme will outweigh any envisaged adverse failure modes.

At worst, fitting an earth tail between the back-box and the socket outlet
earth terminal will provide a parallel earth path in some instances. The
converse could result in no earth path.

Making the earth tail mandatory would certainly remove any uncertainty about
how to interpret the socket outlet/back-box earthing requirements.

--
Spike