Even the "extracted" items in the IGI can have problems. Some baptism registers, for no apparent reason, have only female children listed.
Also, some "marriage" registers have dates from the Banns. The marriage may have taken place much later, elsewhere, or not at all, and such a register does not mention marriages by Licence,
As mentioned before, use the IGI as a hint at what to look for in the proper registers.
Some "proper" registers have problems too - the Bishops' Transcripts rely on the clergyman not getting things wrong. Some clergymen kept two books, attempting to write the same in both, and some spent a week copying things for the Bishop. Errors creep in whichever method is used.
In my direct paternal line, the "proper" baptism register turns out to be a copy from some genuine original register, and has a mistake in the name of my gggg gf. The BTs have his name correct, along with hs birthplace, a whole column omitted from the "proper" register.