Does the Army constantly change the pattern of organizational clothing when it changes personal clothing?

Considering I am wearing my 2nd version of Dress Uniform (I refuse to purchase the AGSU), and my 4th pattern for field uniform (BDU, DCU, ACU, OCP).

That depends on how you define "constantly".

The U.S. Army Center of Military History has some great reference material for a variety of topics and one I came across a few years ago is a "Survey of U.S. Army Uniforms, Weapons and Accoutrements" by David Cole*.

If you REALLY want to get into the nitnoid of how, where, why, then delve into the darkness called "PEO Soldier" and look at the portfolio of the Product Manager for Soldier Clothing & Individual Equipment*. There actually is a rhyme and reason behind the uniform decisions and it isn't just some senior officer or NCO that needs a bullet on their evaluation.
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* https://history.army.mil/html/museums/uniforms/survey_uwa.pdf
* PdM SCIE - https://www.peosoldier.army.mil/Equipment/Equipment-Portfolio/Project-Manager-Soldier-Survivability-Portfolio/

WTF I wore the od wool pants/shirt for every artic like exercise for 23 yrs.