I've read the Wikipedia article "Calendar era", along with several related articles, as well as Ware's chapter "Medieval Chronology" in the handbook Medieval Studies (1976, ed. Powell), so I know many of the varied and multiple and often co-existing chronological methods in the Middle Ages. Searches on "Anglo-Saxon chronology", "A-S reckoning years", and so forth, tend to turn up the Anglo-Saxon Chronicle or references to Bede.
What I have is a universe in which Christianity never caught on in Europe, and the Anglo-Saxons had no kings by name. What I want is the longest possible plausible span of time for reckoning years that would pre-date the Normans, with Bede taken out of the equation. For example, indiction reckoning gives a 15-year span, regnal reckoning up to maybe 60 years, AUC reckoning on the order of centuries, mundane reckoning on the order of millennia.
My guesses are 1) regnally, and 2) with reference to unusual phenomena such as comets, but if there's anything else we know of, particularly of a longer timespan, that would be great. This would include any hypothetical older methods left over by the Romans that might still have been in force and adopted by the arriving Anglo-Saxons, if the Roman impact was that strong, which I doubt.
In the end, I'll just make up whatever works in-universe out of my many options, but I'd first like to know what we know historically.
2. On a related note, do we know what date the earliest Anglo-Saxons would or would likely have used for the beginning of the year?