While the Sanitronic VII is basically the same machine as the 560, 561 and 562, it would not be considered part of the 500 series, just as the C and R series machines that preceded the 500 series are also the same basic machine but also not considered part of the 500 series. 500 is 500!

When the Dual Sanitronic 50 came out with the new two-speed motor, it would logically be considered an all-new machine and, again, not a 500-series.

I do not know what the designations of Sanitronic VII, Dual Sanitronic 50 or Dual Sanitronic 80 mean, other than the addition of the word "dual" was obviously a nod to the new two-speed motor. I suspect that these names were "pulled out of a hat" since they have no bearing on their respective machines in terms of features or release dates.

The only Kirby model designations that ever had any identifiable relationships were, indeed, the 500 series machines. The 500 number corresponded to the year of manufacture.

So, in order for the SVII, D50 and D80 to be considered part of the 500 series, their model numbers would have to have been 563, 564 and 565. But that would only have worked if these machines were each made for only one year, which they were not. The SVII was made for two years and the D50 and D80 were both made for three years.

Hmmmmmm... Kirby seems to have "reinvented" its anniversary date a few times. The Model 516 -- "the first totally new, dramatically redesigned Kirby in over 20 years!" -- was introduced in 1956 and was called the "50th Anniversary Kirby" in company literature.

As I noted in my Kirby 500-series web site, that seems to be stretching the point a little -- granted, Jim Kirby made his first mechanically operated sweeper in 1906, but the first machine to bear the "Kirby" name did not come out until 1935.