It’s not so much the D+7 that matters as to find out the basis for why some are using D+2, others D+7 and yet a few using D+9. Real Clear Politics only records a handful of reliable polls to compute their average.
Gallup came out yesterday and said the party id this year will be R+1. So any national poll with a D+7 sample is not even close to credible.
Furthermore, the TIPP polling firm is sampling about 130 people per day in the rolling average. If you know anything about polling, that is a joke for a national pol - and should be a MOE of about 6%.