One way to approach this problem is to use the
DATEDIF function in combination with
DATEDIF function calculates the difference between two dates in a specified unit (e.g. days, months, years). The syntax is:
DATEDIF(start_date, end_date, unit).
IF function can be used to check if the difference between the "lastUpdated new vs existing" field and today's date is less than or equal to 30. If it is, the contact is considered new, otherwise it is considered existing.
Here is an example formula you can use:
Where A2 is the cell containing 'lastUpdated new vs existing' field.
You can use this formula in a new column next to the 'lastUpdated new vs existing' column and copy it down for all the contacts.