Question about Linhoff Technika ground glass carrier

[Andrew]

here's a question for the people who really know their Linhoff Technikas:

I have a Master, a IV and an old III version 5. The frames carrying the GG looks pretty similar but with minor variations where the GG actually sits.

I'd thought they should all be interchangable and indeed I can see barely any difference when I swap around the frames for the III and the IV
But when the frame for the Master goes on, the focus looks awful so there must be a significant difference

so the question: Are they supposed to be interchangable or do I have a problem with the Master's ground glass carrier?

[This might explain some of the out of focus shots I was putting down to user error!]

addit,
it was just suggested to me that the backs ARE different and I should check my film holders for variation
any comments would still be much appreciated, cheers.

[Bob Salomon]

The gg on the V and MT are zeroed at the factory so lenses and cams can be interchanged between any MT and V. With the IV and older models the gg was not zeroed and the lenses and cams are not interchangeable. That is why a cam for a IV and III has the camera serial number stamped on the bottom. On the V and later this is not done. Linhof service can reset the gg on //iv cameras to match each other so you could then exchange the 001615 gg frame between your IV and MT with no change in focus.