What is the difference between the two noble verses: "And We sent not before you except men to whom We revealed" in Surat An-Nahl, and "And We sent not before you except men to whom We revealed" in Surat Al-Anbiya, and why was the letter "min" (مِن) included in the first and not in the second?

"Min" is an extra preposition used to emphasize negation or something similar to it. It can be omitted to indicate generality, as in the verse: "And We did not send before you," whereas it is mentioned in other verses like: "And We did not send from before you." "Min" was omitted in the verse mentioned in the question because it was built upon the preceding verse: "No city believed before them."