I think there's more to it. It's not just a lag; there's also the issue of people who were still employed, using StatsCan's definition, but not working a sufficient number of hours to make a living and so were eligible for CERB. They were thus not counted as unemployed but were still legitimately eligible for CERB. There's one thing.
There's also the issue of self-employed individuals who were not “unemployed” per se but had virtually no income and still were eligible for CERB.
These are two important factors.