Hello.  Here is a sample.  With this type of formula, I only enter in my dates once even though I'm using the dates entered for multiple fields.  I think this is what you are asking at any rate.  I only enter in the start and end date once, but CR will use it for each field I identify.

From my experience when this would happen, I would pull all dates into a report just to see what start and end dates CR was seeing.  I found that the dates were displaying differently than expected in that situation and had to fix the formula accordingly.  (We have a database system that has dates as text fields in either 1, 3 or 4 different fields and can be 5 to 8 characters long!  )  The formula has worked for me in the past except when the data in the field was not matching the data entered.  Try that analysis first as your syntax appears correct.