There is something fishy about the MM3d development time...

[S.Peelman]

Asriel said:

Or, none of the above and you haven't thought this through.

Maybe Majora's Mask 3D only entered development 12 to 18 months ago? 

Was going to say this. They most likely only started actual work on it a relatively short time ago and the first years only doing some priliminary tasks, simple as that .