I'm sure some have read this cam timing adjustment for a pd (jetta in diy), just wondered if anyone tried this.

TDI Cam Timing Adjustment (for rough idle) How-to (with pics) - TDIClub Forums

Am I right in that they are just adjusting the cam timing using the play in the cam sproket (the elongated bolt holes).

Has anyone checked their value with vag com.

Yeah thats right. Also why a car can seem to run better after a new cambelt is fitted.

However dont play with this unless you know what your doing. Undoing those three bolts without the locking pin in place means you are alterting the cambelt timing, do it too much and you will clatter valves.