luca,
Your best bet is to find someone with old Lenox tool catalogs. These would be a wealth of information regarding the Lenox foray into "perfect handle" tools. Have you tried contacting Lenox regarding historical records? You may get lucky.
But, for now here is what little I can tell you:
H.D. Smith Co. was the original inventor and producer of "Perfect Handle" tools, roughly between 1900 and 1930, when H.D. Smith went out of business, a victim of the depression.
After H.D. Smith went out of business, many other tool companies began copying the Perfect Handle design. This would presumably have been sometime post 1930, and some of these companies are still making them today.
Good luck in your search...