What are the reasons for Imam Ahmad's multiple statements on a single issue?

Imam Ahmad, may Allah have mercy on him, like other Imams, may have more than one opinion on a single issue. This is because he issued fatwas to people for fifty years, during which his knowledge was renewed, and new aspects of deduction became apparent to him. He explained the reason for the variation in his sayings by stating that he would examine a hadith, and if he found something better or stronger, he would adopt it and abandon the previous statement. The variation in his sayings might also stem from a hadith being sound or weak in his view, or from the emergence of a new indication from a text that was not previously apparent to him, or from the differing opinions of the Companions when there was no direct text. The variation in narrations from him might also be due to his companions' differing understanding of his words. Al-Ala' al-Mardawi, in his book "Al-Insaf fi Marifat al-Rajih min al-Khilaf," clarified the method for understanding the madhhab and for preferring one over the other among Ahmad's conflicting statements.