I've read many times, US ebike sales totals are very hard to nail down. We don't have ebike specific import fees/duties or VAT at time of sale. Ebikes come into the US as bikes or general consumer merchandise, in large containers. The real number of 'ebikes' imported aren't generally known. When ebikes are sold, only state sales taxes are paid by the buyer, no different than buying a toaster. And registration of ebikes isn't required in the US. Add kits to the mix and it just gets more murky. In comparison, European sales totals are easy to compile, due to specific taxes, fees, registrations and few kit bikes are allowed.
Industry sales reports are compiled by private companies every year and offered for sale. These are used by the industry to decide what will be imported and offered for sale, among other things. Pete Prebus on the other EBR has written accurately about sales in the past, I don't know, given he's now on the inside with the expo, if that'll continue.