I'm quite sure it's 1918 factory fabric. I helped restore the Jenny now at the College Park Aviation Museum, and we used the NASM one as a pattern (in fact while documenting it I found an old Liberty Bond flyer tucked behind the firewall). For the tapes we used an old pinking machine that NASM had at Silver Hill, and made tapes with the large pinks. So at least in the US it would seem that pinked finishing tapes were being used in 1918.
edit: From the NASM web site:
America by Air , transferred from the War Dep't in 1918.
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