2 Cannalure M276 Projectile

Was given a 7.62x51 M276 purple tip IR/ dim tracer, headstamp LC/10, by a fellow IAA member that had 2 cannelures, not just the normal one or none. He wanted to section the round to see if its truly a M276. Thinking reload, my first impression after pulling the non-magnetic bullet was that it was a .308 FN tracer with the 2 cannelures. It turns out to have the same milky white tracer composition (R440) that the 1 cannelure purple tip (ie: LC/95) or the green over white (ie: LC/92 or LC/70). Red primer and black bullet sealant.
Did the U.S. switch to a double cannelure for the M276 and why?
Thanks wolfganggross

The tracer is an M276 dim tracer. My understanding is that late production M276 have two cannlures as an additonal method of distinguishing them from regular M62 tracers. M276 tracers headstamped with 2008 headstamps (latest date in my collection) do not have the 2nd cannlure which gives an idea of the time frame.