Hey mark!   
      
    ml> systems that display the message's written time in local time or   
    ml> UTC if configured to do so   
      
   I've yet to see any BBS get that right if indeed the BBS software can be   
   configured to do so.  Do you have or know of a working example that indeed   
   gets it right?   
      
    ml> you cannot convert to/from local/UTC if the TZ isn't known   
      
   Understood.  Speaking for myself, I have never bothered and don't use the FTN   
   datetime for anything, nevermind converting it even if only display purposes.    
   What I was taught AGES ago is the data is the data even when it is obviously   
   wrong, and that to tamper with raw data is EXTREMELY vorbotten.   
      
   If I cared, for local display I would do something like this (using the   
   datetime and TZUTC from "MSGID: 1:3634/12.73 5c3e3137");   
      
     TZ=UTC date --date="15 Jan 19  14:13:10 -0500"   
      
   which outputs "Tue Jan 15 19:13:10 UTC 2019" on the machine I am currently   
   using to reply.  Assuming a FTN compliant "TZUTC: 0000" that translates to;   
      
     TZ=UTC date --date="15 Jan 19  14:13:10 0000"   
      
   which outputs "date: invalid date '15 Jan 19  14:13:10 0000'".  However if I   
   add the '+' character to the start of the offset string then it outputs, "Tue   
   Jan 15 14:13:10 UTC 2019".  In other words proper datetime applications based   
   on the strftime function will only work with utc offset data with the correct   
   prefix for east (+) or west (-) of prime meridian.  Your mileage may vary.   
      
   Note that this reply doesn't contain a CHRS control line given that it is pure   
   ascii.  :-)   
      
   Life is good,   
   Maurice   
      
   ... Don't cry for me I have vi.   
   --- GNU bash, version 5.0.0(1)-release (x86_64-pc-linux-gnu)   
    * Origin: Little Mikey's EuroPoint - Ladysmith BC, Canada (2:280/464.113)