Amazon Prime is the key to Amazon’s dominance — period. So when the company reveals any numbers about the shipping and video service, I scoop them up like my 3-year-old does brownie crumbs.

Last year, I pieced together some company announcements to report that Amazon had at least 46 million paying Prime members at the time. Most analyst estimates pegged the number higher than that, but we at least had a firm baseline.

Fast-forward to Thursday. Amazon announced in its earnings release that it added “tens of millions” of new Prime members in 2016. A spokesman confirmed to Recode that these were net additions.

That means Amazon added at least 20 million paid members last year, on top of the 46 million base from the previous year. Amazon now has at least 66 million paying Prime members.

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That’s a big number. That means billions in annual revenue from the Prime fee alone, not to mention the fact that Prime members spend more than non-Prime members. Things sound great, right?

Well, while Amazon did unveil the “tens of millions” addition, it failed to announce the annual growth rate of Prime memberships for the first time since 2013. Hmmm.

In 2014, Prime membership numbers grew 53 percent, the company previously said. In 2015, growth was 51 percent. In 2016? Amazon hasn’t said.

Amazon doesn’t disclose, or withhold, any numbers by accident. There’s a reason, so I asked a spokesman for that reason. He said he’ll have to get back to me, and I’ll update this post if he does.

For now, I’ll have to take an educated guess: Prime membership growth is decelerating quicker than it did from 2014 to 2015 and Amazon doesn’t want to reveal that.

If that’s the case, it’s not necessarily doom and gloom. It’s fair to assume that Amazon is starting to rub up against saturation levels in the U.S., and Prime is still brand new in some huge international markets like India and China.

But if Amazon is worried enough about the perception to not reveal the number, it’s worth noting. Noted.

By Jason Del Rey,

CNBC’s parent NBCUniversal is an investor in Recode’s parent Vox, and the companies have a content-sharing arrangement.