Mussorgsky, Pictures at an Exhibition
An impressive example for the particular value of an urtext edition is to be found in bar 17, top staff, second quarter note of Mussorgsky's Pictures at an Exhibition, a work available in many editions.
The editions by Rimsky-Korsakow (1886) and Paul Lamm (1932), and all following editions give this chord as shown in example 1.
The autograph unambiguously shows two ledger lines and a total of three clearly recognizable note heads; the position of the lowest, somewhat enlarged (touched up?) note head can only be interpreted as g0, presumably even an indistinct concurrence of g0 and a0:
The bottom staff displays an erasure at this point: the f0 was presumably deleted here because it was too close to the chord in the right hand, whereas the hands are never less than a fifth apart in this passage; this, too, supports the reading of the lower note of the right hand as g0 rather than c1.