This paper aims to describe subject-verb agreement patterns within Polish co and który relative clauses in which the relativized subject head noun (virile and nonvirile) modified by a higher numeral is assigned genitive case. Such subjects in Polish obligatorily induce default 3sg. neut. agreement on the main-clause verbal predicate. However, when the same subject is relativized while also being the relative-clause subject, various agreement options may occur depending on the type of relative marker as well as the grammatical gender of the head noun. In order to examine these agreement possibilities, a survey was conducted measuring Polish native speakers’ acceptability judgments. These patterns suggest that both co and który relatives could be derived via a matching analysis because they both allow optionality of agreement in certain environments. Furthermore, this optionality can be accounted for in terms of Case attraction and syncretism of case found in the paradigms of higher numerals and the relative pronoun który.