[tz] Mexico city 1950

Dear Paul I am looking at the timezone for Mexico City 1950. There is a special rules for DST 12 Feb - 31 July 1950, which seems to apply only to Mexico City. I need to find out the definition of the geographic area for which this is valid. You quote as a source http://www.cddhcu.gob.mx/bibliot/publica/inveyana/polisoc/horver/ but I cannot access that source. Do you happen to keep an offline copy of that source information? Best regards Alois