What term works best for unset start/end dates in a range?

I'm rendering information about the date range (or period) that a report was generated from. E.g. from July 1st to August 31, 2018.

Report Period: 2018-07-01 - 2018-08-31

However either the start date or the end date is optional... thus I could have:

Report Period: 2018-07-01 - ??????????

or

Report Period: ?????????? - 2018-08-31

What word/phrase would best fit for the unset start or end dates with "??????????" above? I want to ensure that it doesn't appear to the user that they made an error, which I think "undefined" or similar might imply.