How can we reconcile the mention of numerous angels bringing good tidings to Lady Mary of the birth of Jesus in Surat Aal 'Imran (verse 42) with the mention of a single angel bringing her good tidings in Surat Maryam (verse 17)?

This statement, claiming the Qur'an is contradictory, is a corruption of perception resulting from misunderstanding or obstinacy. Muslims should not debate those who propagate falsehoods before arming themselves with knowledge, and they should leave this matter to well-grounded scholars. There is no contradiction between the two verses. The intent behind "angels" in Allah's verse: (He sends down the angels with the inspiration of His command upon whomsoever He wills of His servants) is Gabriel alone. It is common in the Arabic language to use a plural form while intending a singular meaning. An example of this is Allah's verse: (Those to whom the people said, "Indeed, the people have gathered against you, so fear them"), where the first "people" refers to Nu'aym ibn Mas'ud, and the second to Abu Sufyan and his companions.