While there are several stories/posts in this chart, the last entry (March 2020) is today's focus.
The blue stack represents the difference between my router's reported WAN data and Comcast's reported WAN data. When the blue stack is below the y-axis that indicates that Comcast didn't report as much WAN data as my router did. The long period with significant differences was a problem in my router's firmware (now fixed). Since then my router and Comcast have tracked pretty well.
Until last month (March 2020).
When I went to check my data usage on my Comcast account page, this is what I saw.
Not only was March 2020 significantly low, the first couple of days in April 2020 were zero.
And it stayed that way for several days. Then I figured it out.
With so many people working from home due to the COVID-19 situation, several ISPs have suspended their broadband data caps.
Here's Comcast's statement (archive.is) on March 13, 2020:
Pausing Our Data Plan: With so many people working and educating from home, we want our customers to access the internet without thinking about data plans. While the vast majority of our customers do not come close to using 1TB of data in a month, we are pausing our data plans for 60 days giving all customers Unlimited data for no additional charge.It looks like what Comcast has done is to simply stop collecting broadband data usage.
This lets Comcast "pause" their data caps day by day without having to play with the billing system on the back end. Maybe they'll leave the cap off.