Why do these verses of Rigveda contradict each other on the number of Shambara's forts destroyed by Indra? How to reconcile these differences?
90 forts.
Rig Veda 1.130.7 “For Pūru thou hast shattered, Indra ninety forts, for Divodāsa thy boon servant with thy bolt, O Dancer, for thy worshipper. For Atithigva he, the Strong, brought Śambara from the mountain down…”
100 forts
Rig Veda 6.31.4 “Thou smotest to the ground the hundred castles, impregnable, of Sambara the Dasyu…”
Rig Veda 2.14.6 “Ye ministers, to him who as with thunder demolished Śambara’s hundred ancient castles…”
99 forts
Rig Veda 2.19.6 “…And Indra, for the sake of Divodasa demolished Sambara’s nine-and-ninety castles.”