Can factors like a good interview and recommendation from the nursery school make up for lower scores at the top schools like Dalton, Trinity or Riverdale?

No.  ERB scores are so very important, in fact, they count for at least one third of your admissions profile.  The 3 major components of your admissions file contain: 1) Your child’s ERBs. 2) Your child’s nursery school report, which most likely contains information about you.  And, 3) Your family and/or child’s interview and tour.  At most private schools special consideration is given to children of legacies or who are siblings, admissions preferences often prevail as a respect to the school’s community.