I noted in the Italian book that Landsknecht could be upgrade to melee expert (up to half)
Could we have upgraded Landsknecht and not upgraded Landsknecht in the same unit?
Thanks for the confirmation

No.

The UG size in the upgrade is still 12 bases which precludes this. If it were allowed the upgrade would say something like upgrade 1/2 bases in an UG to ...

Thx, it makes it clearer.