C Fund YTD

So this morning I checked tsp.gov for the C fund YTD %, and it says 14.80%. I figured that would kick me over to 1M, so I logged into my account, and my C Fund YTD is showing 12.98%. Does anyone know why there is a difference? Do they use a different statt date, or is one more up to date than the other. If so, which one is more accurate?