It may be within factory tolerances, but that doesn't mean it is a good coil. I had one bike coil that was low, but within tolerances, however it was hard starting. I had the coil re-wired with an extra 20% of wire and never had a starting problem again.
The fact it is low may indicate that some of the insulation is breaking down inside and it is shorting between windings.
If it still runs and starts fine, I wouldn't worry about it. However, if you begin to have problems, check the resistance again. If it has dropped some more you may have found the problem.