It’s often noted — but seems in another way to be generally disregarded, by Wall Street and media alike — that the terrific sales often touted by Amazon are, well, completely unverifiable. We have the company’s word for it, as opposed to financial filings, that the Kindle has sold as many copies as they say it has, for example. Even though it’s a publicly traded company, Amazon doesn’t release actual figures for anything.

Bu although this has been acknowledged, it’s never seemed to deeply concern investors, nor the many touts high on Amazon stock … until now. In the wake of a huge earnings drop last quarter (see the earlier MobyLives report), which badly shook up Wall Street, analysts have started looking closer at Amazon projected numbers, it seems, and things are … registering ….

According to a story broken by Edmund Lee and Danielle Kucera in this Bloomberg News report, “Amazon.com Inc. (AMZN)’s Prime service, a linchpin of its effort to keep customers loyal and fuel long- term profit, has attracted fewer than half as many members as analysts estimate….”

Citing three inside sources, the report says while many leading analysts — including Citigroup Inc., Needham & Co. and Robert W. Baird & Co. — ”have pegged the current number at 10 million or more,” only “3 million to 5 million people subscribed to Prime.”

As the report notes, it’s disturbing news to investors who believed the Prime program, one of the big reasons Amazon’s earnings have been down, would eventually pull the company out of its earnings slump into soaring profitability:

The slower adoption of Prime adds to concerns about Amazon’s revenue growth. The Internet retailer posted sales of $17.4 billion last quarter, trailing the $18.3 billion predicted by analysts. While the Prime service increases Amazon’s shipping costs, it’s seen as a way to lock in customers and prod them to shop more, according to ChannelAdvisor Corp. Fewer Prime users would mean there are fewer of Amazon’s most dedicated customers.

“A Prime customer is much more likely to start and end a search and purchase on Amazon without bothering to check other channels,” said David Spitz, president of the Morrisville, North Carolina-based firm, which supplies e-commerce software to retailers. The subscribers spend three to four times more than regular customers, said Spitz …

Amazon wouldn’t comment on the report, nor reveal the actual number of Prime subscribers to Bloomberg.

All of which prompted one analyst to note as the horse left the barn, “It drills home the point that you’re paying a premium valuation for this company and key pieces of their economics aren’t disclosed.”

A Barron’s report notes that Amazon stock “took a sharp dive” at the news, but later seemed to recover somewhat … indicating that maybe the news hadn’t “drilled home the point” after all.