copy(m.mapped[start:], data)
				}
				lastValid = m.size - 1
				missing = 0
			} else {
				fmt.Println("Could NOT reconstruct:", err)
			}
		}
	}
	if lastValid == 0 {
		return errors.New("no valid data found")
	}
	if missing > 0 {
		fmt.Println(missing, "bytes missing. Truncating", len(m.filled)-lastValid-1, "from end.")
		out += ".incomplete"
	} else {