How does an adjustment_reasn gets entered into the records on part_tranlog?

Andeus,

Hope I understand your question right.

Manually added Adjustment Reasons (through Code Table) Are accessible in a few ways; 

1.  You can now manually select the new Adjustment Reason when performing a Miscellaneous Adjustment through the Logistics Manager.   The Part Tranlog will then reflect the adjustment reason accordingly.
2. When you execute the Stock Adjustment (Serial or non-serial) MPM either through MPM Import or if called by a Process or Integration;  you can pass the new Adjustment Reason, which then is recorded in Part Tranlog. 

Your mention of Stock Count throws me off a little;  Stock Count posting will, to my knowledge, always post as Source Type “PC” (Physical Count), and leave the “Adjustment Reason” Empty..  Adjustment Reasons only populate when specifically identified in scenarios such as my examples above.

Hope this helps.

Sincerely

-Rudy