score:6
Yes, the CovPass app shows the 2nd booster dose as 4/4.
The CovPass-Check app simply says that it is valid.
All of the applications use the same base source code, so the swiss (and others) should work in the same way as far as the reading and writing of the qr-code is concerned.
The image below shows a portion of the pdf created by the CovPass app: