Define your neighborhood, do a 12-month survey of comparable sales. Arrange the sale dates in quarters of a year. Compare the quarters and you'll likely be able to identify a price trend.
If, for instance, the trend in sale prices has been declining year to date, you should be able to apply a % adjustment to dated sales at a rate supported by your 12-month analysis.
You could also compare a 12-month statistical analysis of your subject neighborhood with other competing areas and derive a locational factor. That is..If there is a fairly similar area with more contemporary close dates you might be able to apply a locational factor using a matched pair analysis.
You could then include your dated comps (with market condition adjsutments) from the immediate area then include more recent sales from competing areas using a locational factor adjustment (along with market conditions adjustment).
If you go outside your defined neighborhood boundaries you better explain in detail....