The concept for "A", a well-known boss song from beatmania IIDX 7th Style, was conceived as early as 3rd Style, but Konami held off because they worried that it would be too challenging of a boss for players at the time.
Unlike most other active BEMANI series, which have ceased the practice of numbered installments, beatmania IIDX alongside Sound Voltex still uses numbers.
System music for the beatmania IIDX sub-series remained absent on original soundtracks until beatmania IIDX 20 tricoro, although tricoro's system music would not appear until the soundtrack to beatmania IIDX 21 SPADA. SPADA itself continued the trend, having its system music appear also on its respective soundtrack.
Another difficulty is sometimes known simply as ana (穴). It happens to be a Double Entendre, as the character is sometimes used to mean "butt".
Marth Debuted in Smash Bros.: Some IIDX songs (especially the ones that crossed over on Extreme, which despite still being an import, is still a more common find than any IIDX machine) are a lot more popular or well-known on Dance Dance Revolution than IIDX. Specific examples have included "A", "Twin Bee(Generation X)", "Xepher", "Last Message", "V" and "Xenon". The fact that most of them are rated 8 and 9 on Heavy or Challenge probably helps.
No Export for You: The series' releases are relegated only to Japan and South Korea. The 5-key beatmania series had a few US releases, under the name hiphopmania. IIDX had a shot in the US with one console release. which tanked. It did, however, come with an improved version of the Japanese official controller, and had a dedicated 5-key mode with classic songs from the original beatmania series as well. The arcade version of IIDX 14 GOLD had a couple location tests in the US, but that was the closest Westerners got to an arcade release.
Importers began to be screwed over further by e-Amusement (Konami's online system, which allows users to use a smart card and user account to save stats/unlocks/the like on games) beginning on 9th Style (as if that version had enough bugs already), leading to only the initial content being available to offline machines due to the e-Amusement dependencies imposed on the unlock system.
Finally, starting with beatmania IIDX 20 tricoro, the game needs a connection to Konami's eAMUSEMENT network for authorization purposes or the game will refuse to run, so even if you somehow import the game hardware, you won't be able to run it. However, there are private third-party servers that allow tricoro to be played without connecting to the official network.
But what about the home versions? Well, there hasn't been one anywhere since Empress.
What Could Have Been: Due to its large number of new songs, beatmania IIDX 20 tricoro was originally going to have its soundtrack split into two volumes—this is evidenced by the title of tricoro's soundtrack, beatmania IIDX 20 tricoro ORIGINAL SOUNDTRACK vol. 1. However, volume 2 never came to be; the tracks that were to be on it ended up in the soundtrack for beatmania IIDX 21 SPADA instead.