Copies of this game got all the way to UK retailers before they were found to be missing their BBFC age rating stamp.

As this was a legal requirement at the time, none of the copies could be sold and had to be sent back, delaying the game's release.

If Naked Snake does not set off any alerts, his codename will be "Tsuchinoko". If the player beats Portable Ops Plus on any difficulty without setting off alert mode at all throughout the game, they will receive a feather for their picture, and Tsuchinoko for their codename.

The Tsuchinoko (ツチノコ) is a legendary snake-like cryptid from Japan. The name tsuchinoko is prevalent in Western Japan, including Kansai and Shikoku; the creature is known as bachi hebi in Northeastern Japan.

"Fortress" from the Metal Gear Solid: Portable Ops soundtrack and "Road Rage" from The Bourne Supremacy soundtrack sound very similar.
Metal Gear Solid: Portable Ops was made in 2007, after The Bourne Supremacy which came out in 2004.