Yep. I've been seeing this all over the place. Numbers aren't complete.
There's a not-so-bad reason for it. Nearly everywhere, the numbers include deaths in hospitals only. In many places care homes are being excluded from the totals. Many countries aren't testing cadavers because there aren't enough tests to go around and doing so would create a giant queue in the morgue.
I heard a couple of days ago that they removed care home deaths from French totals so as to make their numbers more like other countries. This allows comparisons to be made.
So I think US totals may be twice as high, as well.
In the end, they'll probably provide better estimates of fatalities in hindsight by comparing different years and seeing how 2020 looks. But yes, massive undercounting is definitely a thing.