Thanks for the posts, Steve and Nicholas. I've never seen either one before!
I'm still confused as to why Electrolux used a bold wordmark (name without graphic--such as on the Grand Marquise manual), a roman wordmark (such as on the Ultralux manual) and the "boat-shaped" logo (such as on the Epic 6500 SR manual--see reply #29) at the same time. Until now, I'd thought that the first was used only on the commercially-sold machines, the second was used after the "boat-shaped" logo was dropped (which I don't think was ever the case now), and the last was used on the personally-sold machines--at least through the Model 1521s. I've taken for granted, though, that all the Model 1521s were sold door-to-door. Is this correct?