Additional Distinguishing Feature(s) (ADF)
In a few cases where two different (uncorrected) editions of a work yield more or less identical descriptions, reference is made to distinctive ‘non-musical’ elements within their CTs and FLs or to a graphic detail associated with the music text in order to facilitate identification. ‘Additional Distinguishing Features’ of this type are specified according to the exceptional method described under Distinguishing Musical Feature(s), i.e. not in connection with the earliest impression in which each one is found, but under the impression closest to the corrected reprint with which it might be confused (e.g. 6–2a-KI and 6–2b-KI, 9–2-KI and 9–2a-KI, 9–3-KI and 9–3a-KI, 35–1a-B&H and 35–1b-B&H, 71/1–1a-Sam and 71/1–2-Sam). Identification of some impressions is facilitated by the complementary use of ADFs and DMFs (25/1-6–1-W and 25/1-6–1a-W, 32/2–2a-Sam and 32/2–3-Sam); reference to ADFs also proves useful when comparing two successive impressions in the later of which a new plate with music text replaces its earlier counterpart (69–2-Sam and 69–2a-Sam).
 I.e.: ‘Exceptionally, one DMF is used to identify the copies of two different editions whose basic description is identical or very similar; in such cases only, the DMF is specified not in the earliest impression of the edition in which it is found, but in the one most like the subsequent impression with which it risks being confused (9–1c-KI and 9–1d-KI; 66–2a-Sam and 66–3a-Sam; 69–1b-Sam and 69–2-Sam).’