The company ceased operations in late 1962 citing a lack of foreseeable profits. This was largely blamed on tariffs which were said to encourage the importation of foreign dinnerware at prices so low that E. M. Knowles could not be competitive.
Using my resources to look into your inquiry, I was able to find comparable sales that give your 10 pc set of Kowles china in Forsythia pattern from the 1950's a current secondary market value of $150 - $300 USD at auction or in a private sale.
--------- I HAVE 79 GOOD, USEABLE PIECES: 7 DINNER PLATES 10" --- 8 CUPS PLUS 16 CUP SAUCERS/PLATES---8 SOUP BOWLS --- 10 SMALLER BOWLS --- 16 SALAD PLATES 8" --- 12 BREAD & BUTTER PLATES 6" --- 1 SMALL & 1 LARGE PLATER. THESE ARE USED AND MAY HAVE SOME SMALL DINGS. +++ PLUS 3 CHIPPED PLATES. IT IS HARD TO TELL FROM THE PHOTOS, BUT THESE HAVE GOLD RIMS.