On a date field, if I enter "01/01/71" Outsystems automatically and correctly changes the date to:
But if I enter "01/01/70" OutSystems changes it to "01/01/2070"
Where do I change this setting to a lower year when deciding when to add 1900 or 2000?
I don't think you can change this, The 01-01-1970 is a special date in computers, since it is the starting point of the Unix-Time format and a lot of operating systems use this as the default.
When using 01-01-70, you refer to the starting point (day 0) and that is automatically converted to the last day of the automatic year calculation. I think that when you use 02-01-70 (day 1), you will see that it's converted to 02-01-1970.
I would suggest that you stay away from the short year notation and only use the full year notation.