you can be sure of NOTHING from the igi - its function is that of recording baptisms for the dead ! but as a side effect can provide a semi-useful index to the entries in those church records it has transcribed. My own checks on the IGI are that those indicating a transcription from the 'actual' parish register (actually from the official copy thereof) are generally very good - there are errors typically of the form in which a parental name is confused with that of a child - however once you get away from such transcriptions the 'patron submitted' fall into 2 main camps - those which are actually 'official' re-readings of the 1911 official copy - generally ok but a much higher error rate than the 'actual' parish reg transcrptions, and all others in which the error rate is usually quite high and can in places be classed as pure guesswork (I'd go as far to say some are totally incompetent in that two adjacent entries in the parish reg are confused, names misread, dates confused etc etc) - since the official copy is readily available on microfilm PLEASE check this.