When you're planning these things out, yes, things are planned out that far. Project Management for these kinds of things are critical, and the milestones to create a new iPad aren't that flexible.
The items expected in the new iPad Pro (10.5in one)
10.5in screen - technology already exists so it's just a matter of producing one.
A10X Processor - probably has been in development since the A10 went gold
Materials to accommodate the new components - old technology, easy to make
New TouchID sensor, built into the screen - R&D, plus fabrication and implementation would make this a 18-24 month project, so they've had to start this in 2015 to make it come home now.
Working the bugs out - if it's in the April 17 time frame, they're doing that now.
Having said all that, I do think that's the day they move into their new digs, which was an 8 year project.