As you research your family, you will come across a wide variety of resources. These sources will have varying degrees of reliability.
1] Birth records: Birth certificates should be reliable. They are generated soon after the event. Typos or recording errors are possible. Transposed dates, [21 for 12 for example], misspellings [Pratt for Prall], and poor handwriting in earlier records are all possible. If the records are from a church register or town records, the handwriting issue especially applies. When the handwritten records were typed, errors may have occurred as well.
2] Marriage records: Again, these should be reliable. The same errors can apply here that apply to birth records. Marriage bonds, licenses, returns, applications and certificates are among the sources you'll want to look for.
3] Death records: The death certificate is your #1 hoped-for source, but many localities did not require them until the 1880s or later. The name of the deceased, the date and place of death are the three most reliable items here. Although all other information may be correct, it relies on the informant's knowledge of the deceased. The informant could be the spouse, child, sibling or other family member. He/she could also be a neighbor or attending physician.
4] Bible entries: Often the births, deaths and marriages of family members are entered into the family Bible. You may find three or four generations recorded there. Beware of the following:
(a) handwriting - if there are multiple styles of handwriting, then more than one person has made the entries. Dates need confirmation from other sources.
(b) publication date - check the year of publication of the Bible. If the Bible was printed in 1800 and the entries date back to 1720, then someone has copied the dates from another sources. There could be errors!
(c) baptism/christening date vs. birth date - make sure which date is entered. The family may have recorded the dates the children were baptized or christened rather than the date of birth. The former could be a day or two after the birth or a month after the fact. Some baptisms were held off until the parents could get the kids to the nearest church. I have one case where 4-5 of the kids were baptized on the same day. The ranged from about 10 to a few months. Hope that the family has recorded both!