Being largely published in the 1980s, many of the compositions in the books were not computer-proven and so corrections have been reported over the years. For a list of all known errors, please see the Errata pages under each book.
For those books that have been republished after 2000 (currently only Standard 90) I have proved the compositions, mostly in the format in which they appear. This means that they were copied into the desktop publishing software directly and so should not contain any errors. However, there is always the possibility for errors to creep in so I would advise checking them for yourself where truth is important.
I can never guarantee that all errors have been eliminated, therefore I would recommend proving any composition. Peal Prover by Dave Ware and Excalibur by Edward Lupton I have found as excellent tools for this job. The former is free to download, however the latter matches the format of compositions used in the books very closely.
If you find any errors/omissions/typos please let me know using the following form so that they can be amended for future editions and publicised on the website. One of the benefits of digital printing is that relatively small print-runs can be produced and so revisions can be made.