Large date dimensions in SSAS

I would like to share two simple tips on date dimension if the date range in your date dimension is large and uncertain.

A brief background

I was recently working on a project where I was faced with two situations.
1. The range of dates in the date dimension was large. Something from 1970s to 2030 and beyond.
2. The source data can contain dates outside of this range i.e. before 1970 and after 2030 but we did not know for certain the exact range.
So here are the tips.