Check back on the grading description on the website of the business you purchased your pearls from for their specific grading system. If you're talking tissue nucleated cultured freshwater pearls, then yes, I would say it is fine.
I have always felt the grade applied to the whole strand in general, not each and every pearl--but that is something that can be clarified. Grading standards for Tahitians and cfwp will be different, most likely.