The Ninja Gaiden: Master Collection due out in June includes 2007's Ninja Gaiden Sigma, 2009's Ninja Gaiden Sigma 2 and 2012's Ninja Gaiden 3: Razor's Edge - but it does not include Ninja Gaiden Black and Ninja Gaiden 2. Why?
According to Team Ninja, some of the code for those games was irretrievable.
In an interview with Famitsu (thanks, Siliconera), Team Ninja brand manager Fumihiko Yasuda explained:
"As for Ninja Gaiden Black and the original Ninja Gaiden 2, only pieces of their original data were still intact, and we couldn't salvage them either. That's also the reason why we chose Sigma."
Ninja Gaiden Black is a reworked version of Ninja Gaiden that came out in 2005. It's famous for being even harder than the original. Black was released through Xbox Game Pass for Xbox One S and X (with enhancements for X), but was pulled from the subscription service in September 2019.
Ninja Gaiden 2 is an Xbox 360 exclusive that came out in 2008. Ninja Gaiden Sigma 2 is a port of this game first released for PlayStation 3 in 2009. It later saw a launch on the Vita. Digital Foundry analyses Ninja Gaiden 2 in the video below:
In the same interview with Famitsu, Yasuda said Team Ninja considers Ninja Gaiden Sigma and Ninja Gaiden Sigma 2 as "the final versions".