Hello Martin,
On 16.11.19, you wrote,
Looking back at the messages you created with Winpoint, your TZUTC
figure is 0100.  But since you are located in the UK, the offset should
be 0000.
+0000 in winter time, +0001 in summer time :)
I think you meant +0100 for the second entry.  
In any case, if you look back at any of the messages you created with Winpoint, you would find that the TZUTC is *always* +0100 irregardless of the season.
Even if I changed the TZ here on my PC, I could never get Winpoint to register a -'ve for the TZUTC in the messages.  It is as if the author only intended users to be East of the time meridian. LOL.  
But it is most likely that the program miscalculates the resultant TZ figure and does not include the -'ve for the Western time zones.
This looks like another CON candidate to be added on "the list":
     
https://kolico.ca/fidonet/echos/points/
../|ug
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