splitting hears
David,
Maybe you and I are splitting hears here but, the fact is there never was a Kirby model 1C. All the model Cs with the light were "called" 1C's but you will not find a 1C on any Kirby ID tag.
All Kirby C's with or without the light were ID'd as model Cs Therefore Mine is a "so called" 1C by definition, it's a very early 1C, but a 1C none the less, I know that this doesn't fit your slit hole theory but again very little in Kirby history is written in stone.
Jim