The reason that I have trouble accepting 666 as a year is that it renders the copies of Revelation that we have that say '616' as being just arbitrarily unreliable. Those documents, if 666 is a year, compete with our otherwise very good reason to believe that the copying or transcription process that people used when producing newer versions of the originals was sound and of high quality. For a transcription error like '666' turning into '616,' without any reasonable explanation, is to cast serious doubt on our belief that the documents that we do have, accurately reflect the originals to us.
666 being gematria however, explains the 666 and 616 discrepancy satisfactorily. It is when you compute the numerical value of 'Caesar Nero,' written in Hebrew letters, that you get 666. If instead you compute the numerical value of 'Caesar Nero' in either Greek or Latin letters (I don't remember which), you arrive at 616. This explains why there are some copies of Revelation where the number of the beast is 616.