It appears that the Mosaic dietary laws didn’t just disappear over night. I was reading Herman Witsius’ The Economy of the Covenants Between God and Man on “the abrogation of the old testament” (I assume he means covenant). Witsius makes an interesting observation:

But this liberty was for some time not sufficiently known, even to the apostles themselves; till Peter was instructed therein by a heavenly vision, Acts x.11. 5thly. Then, by a solemn decree of a synod of the apostles, under presidence of the Holy Spirit, it was ordained, that a yoke was not to be put on the neck of the disciples besides those few things necessary for that time; namely, to abstain from meats offered to idols, and from blood, and from things strangled; to which was subjoined, though of a different kind, fornication, Acts xv. 10, 28, 29. 6thly afterwards Paul preached freedom from these things also, excepting fornication, that being contrary to the moral law, 1 Cor viii. 4, 8 and x. 25-29. 

Back then they used italics in strange places. I left them here. Oh well, back to studying for Sunday School. Next class is on the civil laws of the Mosaic Covenant.