On Rosh Chodesh we read in Bamidbar 28:4"et hakeves echad..." Shouldn't the grammar dictate there be a definite article on adjectives that modify definite nouns? Later in the pasuk it says "hakeves hasheini."

Also, a few psukim later in Bamidbar 28:7 it says "lakeves haechad." We have support for it being haechad and not echad.