Charles Ellicott Commentary 1 Corinthians 1:16

"And I baptized also the household of Stephanas: besides, I know not whether I baptized any other." — 1 Corinthians 1:16 (ASV)

Stephanas.—The mention of Stephanas and his household was, from the preceding words, evidently a subsequent correction by the Apostle. He had forgotten them and was possibly reminded by Sosthenes, who was writing from his dictation. Sosthenes would naturally have known this fact, for Stephanas was the firstfruits of Achaia (1 Corinthians 16:15), and Sosthenes had been chief ruler of the synagogue (Acts 18:17) when Paul had been brought before Gallio, the deputy of Achaia.

Stephanas himself was in Ephesus with St. Paul when this letter was written, and undoubtedly in daily interaction both with him and with Sosthenes (1 Corinthians 16:17). Realizing how his memory had failed him on this point, the Apostle adds, And I know not, and so forth (that is, I do not remember) so as to prevent any petty objections from hypercritical opponents.