IMHO.

JA as a clergyman's daughter knew all about the law relating to marriages in the early 19th century: her creation ,Mrs Bennet, patently didn't. And as an attourney's daughter this makes her inability to understand all the more comical.

You will probably ahve noticed that Mrs Bennet, thoughout the book, often trumpets idiotic statments about the law, especially with regard to the entail afffecting Longbourn, and her pronouncement about the special license she expects Darcy to obtain is yet another instance of her being a woman of mean understanding and little information , IVHMO.

The bald truth is that Darcy would simply not be eligible for a Special License, and the linked post explains why ;-)