Should any person making improvements on a structure or building fail to report the same to the tax assessor as required above, a penalty may be added to the assessed value of such improvements, and such penalty shall be arrived at by taking 10 percent of the difference between the current assessed value as finally determined and the prior year‘s assessed value of such structure or building. If a structure or building has not been assessed heretofore, has no prior year’s value and is unreported to the tax assessor by the owner thereof, then a penalty of 10 percent of the current tax value as finally determined of such structure or building may be added.