I have a Rolleicord open right now for a cleaning, so it's easy to show you the frame spacing mechanism (Rollei calls it 'film metering,' metering as in measuring)
The notched disk rotates as the film is wound forward. After a distance- the outer edge of the disk- the notched area will allow the tab on the three-pronged metal piece to rotate inward,which then drops the tip at the left end into the ratchet mechanism on the wind knob, stopping the knob and stopping the film from advancing.As you can see, there is some slop in the notch opening and tab sizes.
On your Vb, you can OPEN THE BACK FIRST, then unscrew the center of the counter ring.When you pull that out, you will the backside of the notched disk. And inside the camera you can see the tab sticking into the opening that is in the notch in my photo.
More often than in Rolleiflexes, I have seen some messes inside Rolleicords. Grease and oil where they shouldn't be.Dirt and hair and bugs. All of these can lead to parts moving a little slower than they should, etc. So a cleaning will make frame spacing more consistent.
You can try exercising the camera for a few rolls.If you put an empty spool in the top chamber and close the back it will act like there is film (although rough). Do this for 5-10 'rolls' and see what happens.
By the way, the metering/frame spacing system on the Rolleicord IS slightly rougher than on the Rolleiflex. For example, the size of the teeth on the ratchet that stop the film from advancing are larger, causing more slop (well, ok, they are about the same physical size as on a Rolleiflex but there are maybe 25 teeth on a small diameter while the 'Flex has maybe 100 teeth on a larger diameter, so in effect the teeth are 'larger' on the 'Cord). So the frame spacing on a Rolleicord will be prone to more variation than on a Rolleiflex. But yours sounds like much more than this. 1-3mm variation I would expect; more than that is not ideal.