Birth, marriage and death registries
There are three types of registries, each of them for one of the most importatnt life events, birth, marriage and death. As the registries were originally used only by the church, the records marked there are christening, marriage and burial.
All these three types were usually in one book for whole parish in 17th and 18th century. During the reforms done by Emperor Josef II. it was ordered that each type has to have its own book and each village has to have its own part in the book. However in case of small villages there were all three types (BMD) written in one book in separate sections.
Parish of Nadejkov in State Regional Archives in Trebon (if you click on the link, it will get you to the SRA Trebon website) can be taken as an example of this. First two books are BMD for all villages of the parish, then there is one book just births for Nadejkov villages. After that follow a long row of BMD for each village of the parish and then separate registries for B, M and D for whole parish.
Open and closed registries
Czech law about registries states that all registries older than 75 years (in case of marriage and death) or 100 years (in case of birth) should be in the archives. However that's not always the case. There are so called open registries which contain records younger than 75/100 years. These registries are not stored in archives but in the municipal offices.
There have to be all records in the registry older than 75 or 100 years to transfer the registry into archives. If there is one single record younger than this timespan, the registry stays in the municipal office. Because of this fact many registries which contain records older than one hundred years are still in the municipal office and not accessible for public (only for direct relatives and it has to be proven by birth and other certificates).
Example can be again seen in Nadejkov parish - birth registries are available till 1891 (should be 1911), marriage registries till 1902 (should be 1936) and death registries till 1925 (should be 1936).
Reforms made by Josef II. also stated that all registries have to have indices. These are list of records which the registry contains. Usually are written in alphabetical (by surname) and then chronological order, ie. A 1784-1815, B 1784-1815, C 1784-1815 and so on. Unfortunately there are sometimes gaps, not all records are covered and so on, so if you can't find a person in the index, it sometimes doesn't mean the person isn't in the registry. The one who created it could overlook the record, forget to write it into the index and so on.
The indices can also be complicated because of language specifics - sometimes B and P letters are written together, as well as D and T or C and K. The surnames which begin with J today could be written under G in the registry and so on. Anyway, indices are very helpful when they really exist for the parish.