the usual reason for 2 bapts for same child is mentioned in thread = 1st was a private bapt sickly child) 2nd was the public reception into congregation - some vicars noted both, some only the latter

you should also realise that there are gaps in all parish records for many reasons - sometimes a vicar makes a note but forgets to enter it in reg, some regs are copies with errors in transcriptions - now the actual registers are on line easier to check on these