Datapoint Sango/Indefinite articles
I don't think that the word 'indefinite' accurately describes the word mbeni although it is probably most frequently translated as 'a'. Its meaning is more 'a certain', although translating the word this way is too strong in English. Support for my interpretation might come from the word's etymology: mba, variant mbe, means 'the other.' It is used to mean 'buddy'. (A parallel is found in Gbaya.) The word has been fossilized in mbage (other here) 'side,' as in 'the other side of the river.' Other Ngbandi words have been fossilized in the same way: nzo 'good' = ni determinant > 'good'.
Values 
Indefinite article distinct from numeral ‘one’
- Example 59-100:
-
ala mu mbeni melenge (ti) wali okoala3plmutakembeniamelengechild(ti)(of)walifemaleokooneThey take a girl.
Source: Samarin 1967: 61
- Example 59-101:
-
i faa mbeni kota yakai1plfaacutmbeniakotalargeyakagardenWe made a large garden.
Source: Samarin 1967: 61
- Example 59-102:
-
ala mu na i nginza mbeni pepeala3plmugivenaprepi1plnginzamoneymbeniagainpepenegThey don't give us money any more.
Source: Samarin 1967: 61
- Example 59-103:
-
ambeni avo karakoambenipl.someavosm.buykarakopeanutsSome buy peanuts.
- Example 59-104:
-
mbeni mbakoro wali aekembenicertainmbakorooldwaliwomanaekesm.copThere was (once) a certain old woman.
- Confidence:
- Certain