On Sun, 5 Aug 2018 14:25:21 -0700 (PDT), Davej
wrote:

In a 20 year old house how common is it to find windows
were not properly flashed? The Tyvek is simply cut out
around the windows. It isn't even taped to the window
frames.

What you have is an installer problem. Some clowns install windows by
piece work. $15 per window will get you three fasteners an not much
else, as to quality of the install.

Big window companies will not warranty a window not installed by
instructions, or a trained installer.

A crack head would put one in upside down.