Accidenz (sic) Grotesk was released by Berthold in Berlin in 1898, according to their own literature. It was obviously based on faces already offered by other foundries, some of which were later taken over by Berthold. One of the contemporaries of AG was Royal Grotesk from Theinhardt. In Berthold’s specimen booklet no. 429, which was most likely released in 1954, Akzidenz Grotesk Mager (light) was still referred to as Royal Grotesk, in brackets. Berthold acquired a typeface in 1908, (when they bought Ferd.Theinhardt) which they released as Akzidenz Grotesk Halbfett (medium). They kept adding weights, some of them from other faces, acquired from other foundries. Every foundry had a version of that type of face, more often than not available in a few sizes only. The original series remained quite divers, individual weights showing not much resemblance but in name. It was mainly a marketing and naming success. That only changed when they cut Series 57, and then Series 58, named for the years of release. These had some sizes (but not all) recut under the direction of Günter Gerhard Lange, who was their (freelance) artistic director at the time.
GG Lange always claimed that Berthold had taken some AG weights and sizes from Popplbaum in Vienna, and that is supposed to account for the release date of 1896 or 1898. Popplbaum was not bought by Berthold until 1926. Berthold did take different fonts from all the foundries they bought (and obviously also made deal without buying a foundry) and rename them until they got a family together which still showed the original influences, sometimes even from size to size. The deals between foundries (by 1924 Berthold had bought 17 foundries, in Prague, Riga, Stuttgart, Leipzig, Moscow and St. Petersburg) have never been fully researched, and neither has the complete history of Akzidenz Grotesk been written yet.