Hmm.. I'm not so sure adding "2000" is something we can just assume. This date creation method is used for the value given in the data-value attribute - which is hidden from the user. I'd suggest the developer to just be wiser and use yyyy as the format instead.

Regardless of what's wise, what's not, according to the docs it should work and I wasted 2 hours troubleshooting it.
If you don't support 'yy' in data-value then please state that in the docs.

The yy format is supported the way it should be: displays year as a 2 digit number.

It's just not a good idea to use that format for the hidden value since it's vague and assumptions have to be made. That's the entire purpose of having both format and formatSubmit.

But yes, I agree, this fact should be highlighted in the docs.