A speaker coil is basically a large inductor. As such, the 16ohm reading refers to impedance, not resistance. (Impedance is similar to resistance but includes a phase component) Your meter is reading ohms of resistance. All that being said, I think your 12 ohm resistance speaker is fine.
DC resistance is one component of impedance and usually comprises 2/3 to 3/4 of the total value. So, a DC resistance of 12.2 is in the range expected for a 16 ohm speaker.
My setup is in a cramped spot so I half-assed it and unplugged the speaker cord going into my head and read off that, probably threw the number way off. It's a 1-12 by the way.
There is very little resistance in a short length of speaker wire + internal connections. I doubt if you'd get it to even show on a meter at any setting. Needless to say, this is all part of what the amp sees anyhow so is the most accurate for settings.