All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If one takes many oaths on one thing and then breaks his oath, only one oath expiation becomes due on him according to the majority of scholars. The Maaliki scholars, however, are of the opinion that he should make as many expiations as the number of oaths he has broken, unless he intends (by making many oaths) only confirmation.
According to Ibn Rushd, there is a difference of opinion regarding the case of someone who takes many oaths on the same thing. Some scholars say that only one expiation becomes due on him. Others say that each oath should be expiated except if he intends confirmation by repeating the oaths. This is the opinion of Maalik .
That you delayed the expiation for the period of time you have mentioned requires nothing other than repentance and seeking forgiveness. The expiation does not lapse over time because it has become a right due on you to the needy persons.
Allaah Knows best.