I am confused. For example can we claim a past impact value in the present. why not 5-year IF. Really its usefulness is doubtful. IF is of the Journal not the individual papers published there. individual paper should rather be judged by # citations which do not fluctuate and can only increase.
the impact factor of your published during the that particular time alone stands good. you can never update it , even the journal as got higher impact factor in recent years.