I've not been able to determine a pattern. To me it seems that it's more of a luck of the draw. Example, I buy 3 units from Target, all are 39001s, FU serial and 2D datecode and 2 of them are open and 1 is a closed style.
The closed face style are similar to the KHS-400A and B models in terms of the POT adjusters. With you looking at the underside and the ribbon connector at the bottom, the left POT is for DVD and the right one is for CD media.
I believe on the open style one, it's actually printed which one is the DVD POT and then by process of elimination, the other is the CD POT.
The Yellow PS2 auto-boots all. PS2, PS1 stealth and DVD movies.