There are two different sets of Brock-illustrated editions of Jane Austen's novels. The first set, published in 1898, includes illustrations by both of the Brock brothers, Charles (C.E.) and Henry (H.M.). They each illustrated three of the six novels. Four of the novels (P&P, S&S, MP and Emma) were published in two volumes; NA and Persuasion in one volume each. Each volume has six illustrations; thus, the first four novels have 12 illustrations each, and the last two have six each. ETA: These illustrations were black and white line drawings, which were colored in the production process using (I think) lithography. Thus some of the editions will have more garish colors than the others, depending on the way the coloring was added in the printing process.
The second set of novels were watercolor illustrations by Charles Brock only, distinguished by the softness of the coloring. These are part of the larger set of "Idylls of English Life" series from Dent. Each novel was published as a single volume, with 24 color illustrations, including a medallion illustration on the title page. Later printings only contained 16 of these illustrations. These were published between 1904 and 1910, I believe. Not sure of the exact dates but it was definitely in the first decade of the 20th century.
Charles Brock also illustrated an earlier edition of P&P with black and white drawings. Can't remember how many but there are a lot.
I believe Sourcebooks uses the illustrations from the 1898 set. Harry used the C.E. Brock watercolors from the later editions for his ebooks.
You can see all of the
Brock illustrations (and some others) at a website I created, Molland's. Scroll down to "Novel Illustrations Archive."
(I own several of both editions of these books. I hope to eventually have them all, but the prices have become really outrageous. Other book owners kindly contributed to the illustration archive. Enjoy them, but please note that they are not to be used for commercial purposes.)
P.S. My avatar is Catherine Morland from the C.E. Brock watercolor illustrations of
Northanger Abbey. She is scaring herself with
The Mysteries of Udolpho.
ETA: There are many, many later editions and printings of Jane Austen's novels that include the Brock illustrations. Most are from the 1898 edition.