Why did the Prophet recommend fasting the ninth of Muharram along with Ashura a year before his death, even though the Jews had left Medina much earlier than that?

Ibn Hajar, in Fath al-Bari, answered the question about fasting the day before or the day after Ashura by stating that the Prophet, peace and blessings be upon him, commanded differentiating from the Jews in fasting Ashura by fasting a day before it or a day after it. This was in the latter stages, after he had initially preferred to agree with them in matters where he had not been commanded otherwise. But when Mecca was conquered and Islam became widespread, he preferred to differ from them.