While doing the linear regression analysis on excel state or simply data analysis add-ins., the R2 or R delivered in model output is different from the RSQ or R calculate via excel formulas i.e., =RSQ or =CORREL.
In my version of excel, the built-in functions RSQ and CORREL work correctly in the case of bivariate relationships. It's not clear what "excel state or...add-ins" you might be using, or how you're using it/them, so I can't offer any advice on why the results might differ from the built-in functions.
Could you elaborate, and possibly give the results for a small data set?