Intentionally "creating" a mix, believing that it's offering benefits is misguided, as all lubricants must be miscible, it doesn't mean that things like cold temperature performance (the 0W) part will remain a 0W in the blend.
Being forced to top up with something else isn't harmful per se...but as others have advised, the dipstick doesn't have to read "full" at the end of the OCI.
My Nissan ends up at the add mark at about 7,000km into a 10,000km OCI, so I have to add (this time it was at 5,000km).