Pareus and Wendelin on perfection of parts
Thesis XXXVII. This agrees with what we read in Pareus on Bellarmine's De justificatione, book 4, chapter 11, page 1077: 'In the passages cited, which ascribe perfection to some or require it of all, the perfection meant is not of degrees, the degree of obedience the law's exactness (ἀκρίβεια) requires, but perfection of parts: integrity as opposed to hypocrisy, that is, a true and unfeigned desire and zeal to obey God and to resist evil desires, and a beginning of obedience to all God's commandments.'
Wendelin follows in Pareus's footsteps on this point in his Christian Theology, book 1, chapter 26, explaining thesis 10, section 3: 'The perfection ascribed to the saints is not of degrees but of parts; it is not absolute but limited, and we call it sincerity.'
Indeed it might well seem pointless to cite Reformed testimonies on this matter. They use this distinction of perfection for that purpose so often that few of them lack it.
Latin
XXXVII. Quibus consentanea sunt quae leguntur apud Paraeum in Bell. lib. 4. de Justif. cap. 11. pag. 1077. In locis allegatis, inquit, quae perfectionem aliquibus tribuunt, vel ab omnibus requirunt, perfectio intelligitur non graduum, sive is obedientiae gradus quem legis ἀκρίβεια, requirit, sed perfectio partium, sive integritas opposita hypocrisi, hoc est, verus & non simulatus affectus & studium obediendi Deo, & repugnandi cupiditatibus; atque initium obedientiae secundum omnia Dei mandata. Qua in re quoque vestigia Paraei premit Vendelinus, Christianae Theologiae lib. 1. cap. 26. in explicatione theseos 10. sect. 3. Perfectio, inquit, quae sanctis tribuitur non est graduum, sed partium, non est absoluta, sed limitata, quam sinceritatem appellamus. Verum merito posset videri superfluum hac de re Reformatorum citare testimonia: cum distinctio ista perfectionis in illum usum adhibita, tam frequens sit apud eos, ut pauci sint apud quos reperiri non possit.