I've seen a 616 from time to time. Someone (I don't recall who) said it corresponded to the American 518. However, that doesn't make sense if Canada followed the same model number system as the American Kirby did.
It would seem to me that the 616 correlated to the 516, not the 518. But what do I know...!
P.S.: Also, this 616 has a silver handle lock whereas it was changed to red plastic on the 518.
And, if I am not mistaken, the 518 was the first model with the ribbed middle handle section and silver-speckled bag, This 616 has a plain handle section and plain bag.
Yes, the 518 was the first to have this update and several others, such as the treaded wheels and the version of the cloth bag with the speckles on it.