Create Dynamic Excel Data Validation Lists Using Table Spill Ranges

Excel validation lists avoid blanks and errors with TOCOL(ignore) plus FILTER; the spill range stays stable across worksheets.
How-To Geek on MSN

Forget INDIRECT: The modern way to create cascading drop-down lists in Excel

Use dynamic arrays and tables for fast, scalable cascading drop-down lists in modern Excel.
How-To Geek on MSN

You need to know what the hash sign does in Excel formulas

Smash the hash in a flash!