Hi Sal,
Here is a case to illustrate what I have seen. I did this procedure shortly after the EHC meeting in Glasgow. At that meeting there was a lot of enthusiasm for big balloons and having to break the annulus using cutting wires if needed. I was not using IVUS at this time.

Used a 14 mm balloon. Needed a cutting wire to get the balloon to inflate to profile.
Patient had significant improvement in symptoms. US of left IJ below is at 1 month. Right side (not shown) looked great. Patient still doing well. US shows severe luminal loss in the left IJ at the venoplasty site. There is thickening in the vein wall (?edema). No thrombus.

and

Patient continued to do well clinically for 9 more months, with gradual worsening in the last 2 of those months.
Venography and IVUS below of the left IJ


The stenosis/restenosis is due to luminal loss in the size of the vein. Not intimal hyperplasia or recurrent/undertreated valves.
I have seen this mode of failure more commonly than recurrent valves. This has to be from too aggressive of a venoplasty.