We do pull your retrospective data from some of the vendors (e.g. Fitbit, Withings, Misfit).
However, for example, with Garmin and Polar not syncing your device to your original app (Garmin Connect and Polar Flow) or with Apple and Samsung not opening the inKin mobile app will result in losing data for those dates.
Please use our manual log feature to log that information. Note that if a contest does not allow manually logged data, it will not be reflected in your results.