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Stephen Greenfield asked when Los Angeles converted to 2L-5N.
I've read that Los Angeles introduced NEW 2L-5N exchanges and numbers by the mid-1920s, alongside existing 2L-4N. Both 2L-5N and 2L-4N co-existed for many years in Los Angeles, until the 2L-4N numbers began to be converted to 2L-5N sometime during the 1950s as standardization in preparation for ultimate inbound customer DDD to Los Angeles.