Note that the release times for these private surveys are the official embargo times. The releases are provided to subscribers much earlier and typically leaked to the rest of the market long before these official release times. Mitsubishi is typically leaked by 8:00 ET, and the Redbook survey is usually known in the market by 14:15 ET.
The Mitsubishi chain-store sales index is based on a representative sample of nine large retailers and measures sales on a weekly basis. The index is relatively volatile from week to week and therefore has little to say about broader consumption patterns. Mitsubishi also produces a monthly measure of sales, which does a better job of predicting a few pieces of the retail sales report (particularly the general merchandise and apparel components).
The LJR Redbook survey tracks 15 retail stores every week to determine the changes in sales. The report is month to date where: the first week of the month is compared to the previous month; the second week compares the first two weeks of the month to the previous month, and so on. The Redbook survey has a somewhat better track record for predicting chain store sales in the monthly retail sales report.