Ok. So here is a massive update to the charting, sales and such that could also open an explanation to a few mysteries.
World Wide album sales (officially documented by RIAA, Billboard, etc.)
------------------------------------- Worldwide sales ---------USA Sales ------- Europe Sales ------- Total Sales for Singles
Iron Maiden -------------------------- 4,175,000 ------------ 685,000 ---------- 2,315,000 ----------- (4) 335,015
Killers --------------------------------- 4,855,000 ------------ 955,000 ---------- 2,715,000 ----------- (3) 182,500
Number of the Beast ----------------- 8,330,000 ------------ 2,385,000 -------- 3,940,000 ----------- (5) 865,000
Piece of Mind ------------------------- 6,615,000 ----------- 2,340,000 --------- 2,580,000 ----------- (2) 455,000
Powerslave ---------------------------- 5,610,000 ----------- 1,730,000 --------- 2,455,000 ----------- (2) 430,000
Somewhere in Time ------------------ 5,290,000 ------------ 1,765,000 -------- 2,195,000 ----------- (2) 330,000
Seventh Son of a Seventh Son ------- 4,815,000 ------------ 1,210,000 -------- 2,480,000 ----------- (4) 740,000
No Prayer For The Dying ------------- 3,010,000 ------------ 795,000 ---------- 1,495,000 ----------- (2) 330,000
Fear of the Dark ---------------------- 3,615,000 ------------ 480,000 ----------- 2,025,000 ---------- (4) 240,000
The X Factor -------------------------- 1,410,000 ------------ 195,000 ----------- 730,000 ------------ (2) 85,000
Virtual XI ------------------------------ 1,185,000 ------------ 155,000 ----------- 650,000 ------------ (2) 52,500
Brave New World --------------------- 2,290,000 ------------ 380,000 ----------- 1,115,000 ---------- (2) 175,000
Dance of Death ----------------------- 1,490,000 ------------ 230,000 ----------- 880,000 ------------ (2) 125,000
A Matter of Life and Death ----------- 1,440,000 ------------ 270,000 ----------- 850,000 ------------ (2) 100,000
The Final Frontier --------------------- 1,120,000 ------------ 205,000 ----------- 655,000 ------------ No singles released
The Book of Souls -------------------- 1,090,000 ------------ 200,000 ----------- 660,000 ------------ (2) 16,500
Senjutsu ------------------------------- 480,000 ------------- 110,000 ----------- 280,000 ------------ No singles released
Iron Maiden released a handful of singles over the years and individual data is available but here are the most interesting facts about them. The number (4) in parenthesis represents the number of singles released for the album
1. Wrathchild only sold 5,000 copies as a single by itself but sold 130,000 copies when originally released with Twilight Zone
2. Number of the Beast had 5 total releases including the live and studio version of Run to The Hills, also re-releasing in 2002 and sold 65,000 copies in 2002 as a single studio version. Collectively, RTTH sold 585,000 copies
3. Can I Play with Madness is their best selling single after Run to the Hills with 335,000 individual copies being sold of it
4. Excluding live single releases, Seventh Son has the best single single collectively as an album
5. Seventh Son sold significantly less than Somewhere in Time in the USA but is the opposite in Europe where it sold more but Somewhere in Time collectively, sold more overall.
6. The Book of Souls was Certified Platinum by RIAA standards in 2019 as having sold 1 million copies worldwide.
7. Senjutsu, although released in 2021, is their worst selling album of all time although charting at #4 when debuting.