Problem: According to Numbers 26:64–65, all the unbelieving generation of Israelites died in the wilderness, with “not a man of those who were numbered by Moses” remaining to go into the Promised Land. However, when Moses spoke to the people at the end of the wanderings he referred repeatedly to their being witnesses to what happened before the wanderings (cf. Deut. 1:6, 9, 14; 5:2, 5; 11:2, 7).
Solution: First of all, in Deuteronomy, Moses is addressing the nation as a nation and, therefore, may not be making a distinction between individuals in the earlier period as opposed to those in the later period. Second, there were a large number of women present who had personally remembered the things to which Moses referred. Third, both the Levites and those who were under 20 years of age before the 40 years were exempt from the general pronouncement that none of the men would enter the Promised Land (Num. 26:64). So also were Joshua and Caleb, who had been faithful spies (Num. 32:12). So there were plenty of people present who could witness to what Moses was saying, even though a whole generation of men (above the age of 20) had perished in the wilderness, as God had said.