Hello! I know I am quite late to the party, but could you explain what you mean with "not consistently"? I'll just offer some general advice in the following:
Usually, you can manage how (and if) dates are displayed under "Options" on the menu on the bottom of your screen: You can manage if both or only one of them is displayed, what date format is used and whether you want life dates to be displayed as "Born 1949" and "Died 2008" or "1949 - 2008".
When adding life and death dates, you can always choose whether the added date is exact, approximate, a "Born before", "Died after" or a date range. If you have someone "Born approximately" this will be displayed on the tree with this specification, and you'll need to change this manually for every person if you are bugged by this.
