The FDA didn't exist in the US back then either - I don't think the concept of having the government set standards for food & drugs was even thought of until the late 19th or early 20th c.

You're probably right about the strength or dilution of the laudanum depending on who was compounding the tincture - perhaps Mrs Austen's apothecary made it highly diluted, which may explain why she did not apparently suffer such ill effects from its use.