We are always very careful to make sure that the quotations on which the Dictionary depends are accurate.
Slips are wherever possible checked against the works from which they are taken. This is necessary as a slip may have been written fifty or more years ago, based on an edition which has now been superseded, and, as a result, may preserve a reading that is in some way faulty, such as a misreading of a manuscript. The Dictionary has an extensive research collection of books of its own, supplemented with material derived from the Bodleian Libraries' collections and other Oxford libraries. In addition to these resources, quotations may be verified against digital facsimiles of texts such as those available on MEMSO and archive.org. While we rely on printed editions where these exist and are reliable, we consult original manuscripts when we need to.
As well as checking slips taken from printed editions, we try to check those derived from documentary evidence where possible. We ourselves regularly check documents in the National Archives, the British Library, and the university and college libraries of Oxford and Cambridge, but for other libraries and archives — cathedral archives such as York and Durham, or local record offices such as Hampshire — we are greatly indebted to the many local archivists and librarians who have kindly and patiently checked quotations and references for us.
Regardless of whether the source is a document or a literary text, and whether we have found the quotation among our slips or through our searching of electronic databases, the aim of our verification is not only to ensure that the quotation is accurate but to make certain that we have correctly assessed it in its context for its grammar, sense, and, if relevant, its allusions to other texts or references to other items that we have also documented in the Dictionary. In addition we need to confirm some factual information about the source, such as its date, text type, provenance, and the precise form of reference to be used (e.g. a line, page, folio, or chapter number) so that a user of the Dictionary could trace it if desired.
Verification is an essential part of forming a view of the usage of a word in drafting the entry. Sometimes, however, it reveals that a quotation has to be discarded, e.g. as a faulty reading or because the word turns out not to be Latin but a vernacular intrusion within a Latin text. Occasionally, this has a more dramatic effect and causes an entry to have to be rewritten or even discarded entirely. Much time and ingenuity was expended in trying to work out a possible interpretation for sextulatio … granorum, found on p. 164 of the first volume of Extracts from the Account Rolls of the Abbey of Durham (Surtees Society XCIX), before a check by the Durham archivist revealed the sadly prosaic truth that the word was serculatio (‘cutting, reaping’)!
Alongside verifying individual quotations, we keep our whole corpus under review. Sometimes whole authors and works are removed (or added) as a result of this. Recent research, for example, has suggested that Paulus ‘Anglicus’, author of Speculum aureum de titulis beneficiorum (1404/5), was not English at all but probably either Petrus Wysz or Paulus Wladimiri — from Poland.