The indexes were known as calendars, and the term is still in use for these documents in many publications on the records of the Prerogative Court of Canterbury and other courts with probate jurisdiction. The majority of the indexes or calendars cover a single year, and they list the names of the testators and intestates of whose estates grants of probate and administration were made in that year.
As a general rule the surviving paper calendars, compiled for the Court's own use, for some years in the seventeenth century and the first part of the eighteenth century are in PROB 13, while those for the second part of the eighteenth century and for the nineteenth century (until the abolition of the Prerogative Court of Canterbury in 1858) are in PROB 15
Most of the calendars in PROB 13 also list sentences promulgated by the Prerogative Court of Canterbury, either in a separate section after the section for surnames beginning with the letter S, or at the end of the volume. Sentences are often omitted from the calendars in PROB 12 and PROB 15. There are no calendars in PROB 13 for the years 1801 to 1858, but these years of the Court's existence are covered by calendars in PROB 15 and PROB 12
Many of the calendars in PROB 13 (as in PROB 12 and PROB 15) bear on their covers the names of the will registers in PROB 11 which they index.
Many of the indexes in PROB 13 were transcribed to produce the working indexes to wills and administrations in PROB 12 and in PROB 15. However some of the calendars in this series are transcripts of other in PROB 15
Each page of the volume was divided into two columns, and the names of testators were written in the left hand column and the names of intestates in the right hand column. At a later date the information in these calendars was transcribed into other calendars, and the transcripts were made available to searchers as a means of reference to wills, probate acts, and administration acts.
The calendars in PROB 13, in common with the calendars in PROB 15, can be used to supply defects in the PROB 12 calendars. If for instance a PROB 12 calendar does not supply a quire reference for a registered will, or the relevant monthly section of an act book does not contain a particular probate or administration act, it is sometimes useful to consult other calendars for the same year in PROB 13 and PROB 15. Nevertheless it will often be found that an obscure or incomprehensible entry in a PROB 12 calendar has been copied verbatim from an identical entry in a PROB 13 or PROB 15 calendar, and that nothing is gained by consulting the calendars in the latter series.
Most of the calendars in this series also list sentences promulgated by the Prerogative Court of Canterbury, either in a separate section after the section for surnames beginning with the letter S, or at the end of the volume. Sentences are often omitted from the calendars in PROB 12 and PROB 15. There are no calendars in PROB 13 for the years 1801 to 1858, but these years of the Court's existence are covered by calendars in PROB 15 and PROB 12
The conventions used by the compilers of the calendars in PROB 12, PROB 13, and PROB 15 are largely identical.
The dates given in the PROB 13 list are the dates that the calendars cover and not necessarily the dates of compilation. Nor does the list generally indicate the coverage of the calendars in the series. As a general rule it is not until the post Restoration period that it is possible to be confident that a calendar includes both testators and intestates, and that it was supposed to cover all the Court's grants of probate and administration for the year it covers.