For example, according to RIAA Iron Maiden's The Number of the Beast went only one Platinum in the US, and I don't belive it's true because that album has sold over 14 million copies worldwide, so it's hard to believe that it hasn't sold at least 2 million copies in such a big market as America to this day, since it was a very popular and hyped album at the time.
Let's start with a couple basic points:
1. You don't live and never have lived in the United States. Right?
2. You aren't of an age that you could have had any awareness of what was going on with respect to TNOTB "at the time." Right?
So...what exactly is your basis for stating so conclusively what things were like in the U.S. in the early '80s?
As someone with far better perspective than you about such things, let me assure you that TNOTB was neither "very popular" nor "very hyped" "at the time." Prior to TNOTB, Maiden was a nothing artist in the states. TNOTB was released in March 1982. Maiden never played in the U.S. prior to 1981, and, in 1981, played 40 shows in the U.S. - primarily as an opening band for UFO. Even if someone in the U.S. liked Maiden prior to TNOTB, they were unfamiliar with the new singer on TNOTB (who was not yet with the band on any of its U.S. dates in 1981). Certainly, TNOTB had success in the U.S. "at the time," but Maiden was still an opening act at that point, and metal was not all that popular in general. TNOTB didn't even get certified Gold until after POM was released, and it didn't get certified Platinum until after SIT was released.
I also find it amusing that you're blindly accepting whatever source told you that TNOTB has sold 14 million copies worldwide but are doubting the RIAA certification number. What's your source for the 14 million sales figure?
I too would be surprised if, at some point in the last 35 years, TNOTB hasn't sole another million copies in the U.S. (if for no other reason that folks have replaced their original vinyl and cassette copies with CDs and, in some cases, have re-bought a vinyl copy). However, Stadler's point is well-taken,** and it wouldn't surprise me if Maiden and its management have no real interest in jumping through hoops for RIAA certifications.
The Rolling Stones have had a longer career in terms of years, but Strait has released the same number of studio albums. I think it's also reasonable to believe that Strait's fans are more likely to buy all his albums, including each new one as it comes out, while the Stones' fans are more likely to buy only the albums of a certain, "classic," period.
Moreover, the Stones weren't really an album band; they were a singles band. I'm not a fan, but I was surprised that I didn't know any more than two (maybe three) songs on any Stones album.
I think it's also worth pointing out that the Stones have only released four studio albums in the last 30 years, whereas (if the info on Wiki is accurate), George Strait has been consistently and regularly releasing studio albums for 40 years.
** - If you look at the RIAA data for Stones albums, four of their early albums that hit Platinum status (Out of Our Heads, Aftermath, Beggars Banquet and Let It Bleed) hit that status on the same date: October 20, 1989. Their next set of albums (Sticky Fingers, Exile on Main St., Goat's Head Soup and It's Only Rock 'n' Roll) received their Platinum certifications on May 31, 2000. Starting with Black & Blue, Stones albums got their initial Platinum certifications around the time they were released (although many received subsequent certifications on...you guessed it...May 31, 2000). Pretty clearly, these 1989 and 2000 certifications were the result of pushes made by the band management and/or record companies.