it's only the unreliable John Thorpe whose the source of the idea in NA2 of Mr Allen's fortune from trade-you and I and other posters here know That! :)
But, is John's unreliability clear to a contemporary viewing audience, many of whom won't be familiar with NA or the Regency era ?
That's why it seems relevant to question the relevance of NA2's idea about Mr Allen being in trade. JA particularly describes Mr Allen as the main property owner around Fullerton.
Also, changing Mr Allen into a retired tradesman changes the social class of the Allens. I doubt JA intended Mr Allen to be like Mr Weston, who we know makes a trade fortune and retired to purchase his estate. Mr Allen seems to be a large landowner and very rich.