Sorry, I have been away for some times.
–> First option: I got vmx0, vmx1, vmx2 and vmx3. After adding the new NIC, it appears as vmx4 and the existing NIC remain unchanged.
Edit: I tried adding a different type of NIC (E1000 instead of VMXNET3) and both scenario worked. So I guess you are right, it is somehow related to the interface naming scheme.