That patent was filed in 1945 and awarded in 1950 so that at least gives the time frame of when that style was invented. I really don't know when they started using them. I have seen them on drums for a wide range of years.
https://patents.google.com/patent/US2517124?oq=2517124
Page 41 of the number 55 WFL catalog sure appears to show the plastic ends. These are illustrations, not pictures however.
[ame]http://drumarchive.com/Ludwig/1955_WFL.pdf[/ame]
Page 45 of catalog number 51 appears to show metal ends.
[ame]http://drumarchive.com/Ludwig/1951_WFL.pdf[/ame]
Page 72 of catalog number 62 states- "Metal snare plates available on models A through P, specify if desired" This option was not mentioned in earlier catalogs.
All of the three hole snares are listed as being for the "New Classic" strainer which was the P-87. One screw held it on the strainer side and two screws on the butt side for the extended butt or conventional string for the standard butt, so that would seem to explain the extra hole. It is very possible that they used the mold or three hole metal ends for three holes one some wires that were designed for the normal P-83 strainer, at least in some cases. They still work, there is just an an extra hole.
[ame]http://drumarchive.com/Ludwig/1962_LUDWIG.pdf[/ame]
Page 96 of catalog number 64 states it a little differently- "Snares with metal end plates may be ordered by adding the letter M after each stock letter."
[ame]http://drumarchive.com/Ludwig/1964_LUDWIG.pdf[/ame]
It appears that WFL was using metal and then came up with the "new and improved" plastic ends in 1950. As we all know, plastic breaks so by at least by 1961 when catalog number 62 was printed, they had started to offer the metal ends as a option, probably because the plastic ones were problematic.