Often when we wax nostalgic for certain eras ('50s and '60s, '60s and '70s, et cetera) we tend to embellish or distort reality. Such is the case with the term Coronet as being mainly a '50s and '60s term. In addition, I have never heard of a Coronet vacuum cleaner and could not even find one in online searches.
A 'coronet', for those who may not know, is a small crown worn by nobles and peers. In reality, companies have used the name and/or symbol for a variety of products prior to and thereafter the '50s and '60s from Dodge Coronet automobiles, manufactured from 1949 to 1976, to the Smith-Corona Coronet typewriters produced in the '60s and '70s (albeit no specific data could be procured)----a 'corona' being a set of concentric circles around a luminous body such as the sun or moon.
Interestingly, Electrolux Corporation (later Electrolux LLC) included a symbol of a coronet on its 1990s vacuum cleaners such as the Genesis LX, Genesis LXe, Ultralux LX, Diplomat LX, and Ambassador IIIs--the suffixes of each featured in red characters within the gold, silver, or blue coronets (seemingly to indicate the new lighted power nozzles).
Here are some internet photos showing the variety of ways the term 'coronet' has been used by companies over the years--beyond the mid-20th century: a 1965 Dodge Coronet, a Smith-Corona Coronet typewriter, an image of the Coronet Film logo (used in various forms from 1946 through the 1970s), a Knox brand projection screen case label, and a Diplomat LX name stamp:
