Stewart.. If the Municipal engineer produced the plans then he will be the most qualified to advise about extra floors etc.. That`s his job.
Looks as though you have used less rebar than us but as its 20mm grade perhaps that compensates for your particular design??
I`m no engineer and cannot advise on structural integrity.
I doubt very much that a municipal engineer will sign anything substandard or not issue you future permits to go upwards one day...(if initial plans allow)
Cheers,
Fred.