Maybe the disccutters were not Herrenknecht. You know how it works. First x meters you use disccutters of the TBM manufacturer. So maybe first x meter they used Herrenknecht disccutters and then switched to an after...
pretty imressive. I heard that it hasn't been a smooth ride all along. I heard they had to change a lot of disccutters along the way. Like I heard 20 disc cutter every single day had to be replaced!
When I was visiting Bergen in 2017 for WTC, a Norwegian professor told me the same thing about the disc usage. Anyways they made it! Let's look at the final result. Quite an accomplishment.