Coverage window

Suppose a strategy pairs a broad US equity ETP with about thirty years of prices and a thematic ETF that launched five years ago, and the backtest starts twenty-five years back. Inside the run the equity ETP is covered from the first day; the thematic ETF covers only the last five years. Four-fifths of the backtest's calendar therefore predates the second instrument's coverage window entirely, and only those last five years test the pair as designed.

The headline CAGR and max drawdown are still reported over the full window, so a reader who does not check the ETF's first price date will attribute two decades of behavior to a combination that could only have run for five years of it. Reading the coverage windows first tells you which figure you are actually looking at.

Because an instrument has no prices to contribute on the dates before its coverage window begins. Nothing about the run is invalid, but only the stretch that sits inside every instrument's coverage window tests the full set you designed on real prices for all of them. The shortest coverage window among your instruments is therefore the real limit on any strategy that depends on all of them.

This is easy to miss because Fincanva does not move your chosen simulation start year forward to match a short coverage window — the year you enter is the year the run starts, so the mismatch is not announced at the moment you choose it. Metrics are still computed across the whole window you asked for, which is exactly why a long-history headline figure can belong to a strategy that could only have existed for part of it. Check the first price date of anything recent before reading a long-history result.

No strategy can read prices from before an instrument existed, however early the run starts.