I am NOT an expert. It does appear to be complicated.
We know light level has an impact.
We know that birds in their first year of age who start laying before winter will generally lay right thru - so there's an age component.
A bird that goes into molt during winter will likely stop laying, or significantly reduce laying, while a bird that completes molt in fall and starts laying again will likely lay right thru (albeit, at lower rates, since egg production tends to drop with age). So the factors that affect molting have some (at least secondary) impact.
Obviously, there are dietary concerns as well. Annd while I am aware of no diet that triggers laying, or causes laying to persist in the face of falling light levels (winter), there are plenty of dietary things that are known to reduce laying. {I'll leave it to others to debate whether the 1-3% gain in frequency and size associated with an 18-20% protein feed is in fact "a gain", or if the 1-3% decrease in size and freqeuncy associated with the more common 16% protein feed is ain fact a "loss" considered acceptable due to the larger savings in feed costs... As Obi Wan says, "what I told you is true. From a certain point of view."}
And there *may* be a genetic component. Brahma, for instance, are supposed to lay thru winter pretty consistently. I can't tell with mine, their eggs look too much like everyone else's - but whether that persistent rumor was ever true or not isn't something I've seen studied. The few breeds famed for "winter laying" were never high quantity egg producers in the first place, so they have no commercial value as layers, and thus, no money spent studying them.
Funny thing. Becky Brahma laying three eggs a week, every week, produces 156 eggs a year. Ophelia Orpington could produce 4 eggs a week for nine months, then take the next three months off, and produce the exact same number of eggs - so eating Ophelia at the end of the season saves feed costs (a lot of them - Brahma can eat!) and costs you no eggs. Ophelia likely started laying earlier, too. (Numbers for illustration modern Brahma and modern Orps, on average, should both produce more eggs than that in a year, on a preoper diet and with good care).
