Transferring US shares to UK Executors/Beneficiaries

Given this some more thought and tried to think of a solution that is rationale, robust, simple to apply and cost effective!
I noticed that there are two reciprocal agreements in place between the UK Government and US Government:
Reciprocal agreements - GOV.UK (www.gov.uk)

US-UK RDP MOU signed 22 Dec 2017 USA003826-17.pdf (osd.mil)

In the latter agreement they have a reciprocal auditing agreement where neither party will duplicate the work of the other. This seems very sensible!

So got me thinking just where did the ‘medallion signature’ process come from and who makes money from it?
Also why is there no reciprocal agreement in place between UK Probate Courts and US Probate Courts, and what is the process for lobbying to get a change in process (including acceptance of grant of probate documents after the 60 day period (US Computershare dont accept after this 60 day period from date of issue)) ?

Thanks.

John Horner.