thank you very much for your time to clarify this,
this also means that the COS can be issued while I'm in the UK, am I right?

if I'm in the UK and will change the type of my visa from teir 2 dependent to teir 2 general , do I wait for the COS issuance before cancelling my current visa and then go back home country and apply for the new visa? or the COS can't be issued while I'm in the UK, or while I have a valid visa?