I have no expectation that the generic ODB tools and smartphone software is going to do anything other than guide me to worry or just accept a "burp" triggering the engine management light.

Driving to slow (not heating the cats etc) is common and so the error can be ignored. Drive it hard, switch off, drive it hard switch off and next run it should clear.

The free version of most software will be able to allow you to read the errors.
If you pay for it then you should find it allows you to "clear" the error.

Technically I don't think it deletes it, it clears the warning that the error triggers but the error remains in the history log.

Given the car is a mixture of several products (Aero - BMW Engine, Saab in some places and Vauxhall have also been mentioned for bits.) I do not think that selecting a specific donor vehicle. I tried selecting BMW 5 series E60 (2003-11?) for our Series 2 4.4L V8 system and the engine warnings seemed to make some sense. The EML light went off when I sent a reset following a bit of heavy right foot.

I do not ignore the EML as some people do. The 4.4 and 4.8 V8's do have some known problems and are very expensive to replace.

Everyone loves a Morgan. Even me, unless it's broken again.