I don't collect these vigorously, but have a few in collection.
(1) scott 348, perf 12 guide line pair. Any clue to help determine authenticity? Seems so easy to just perforate some imperf version (343).
(2) not sure. I think 412. perf 8 1/2 vertically. Is this how they were produced. I rarely see multiples, just singles and pairs? Maybe its some other number and I'm just missing it.