Some individual hens lay below average, some lay above. If you have more hens that lay above average than lay below you will get more eggs than the breed average. It can work the other way around.
Breed averages are calculated in certain conditions. You may not have those conditions.
Breed average is over a year. Laying goes in cycles. During parts of that cycle they may lay more, other parts they may lay less. Their age, time of year, how you feed them, whether you have severe summers or severe winters all plays into that.
Strain has a lot to do with that. If the person that selects which chickens get to breed uses egg laying as a criteria then you get chickens that tend to lay well, regardless of the breed average. If someone is using different criteria, such has how they look instead of how they lay to choose breeding stock, then laying a lot is less likely. Even if they don't do it on purpose hatcheries usually fall into that group of better laying. The more eggs a hen lays the more of the chicks are from her eggs so those genetics get passed down more often.
If you keep them long enough they will molt. The vast majority of hens stop laying entirely whole they molt, which could be anywhere from one month to four or even five months. How is the molt factored into the breed averages you see?
Will yours go broody? They don't lay while broody. How is that factored in to the averages.
You asked for cautions. Enjoy it while you can but prepare yourself for days and even months where they lay a lot less than their average daily number. If you keep them long enough that will happen.