Varied sized eggs or multiple synchronized layers?

[gingerviolinist]

I've been getting a duck egg every day except twice for about 3 weeks, and 1 day there were 2 eggs! (Perhaps I could have missed one and then found it.) I've gotten duck eggs from 53g to 105g during this time. First egg was 72g. Smaller eggs have been gathered after larger eggs and vice versa (not progressively getting larger). I have 2 pekins that are 28 weeks old and 2 blue swedish that are 18 weeks old. They receive 15 hours of light daily including supplemental lighting and are on Mazuri Waterfowl 50% breeder and 50% maintenance feed. Is it possible that I might have more than 1 layer and they have a synchronized laying sequence worked out or is this just 1 duck laying widely varied sized eggs daily?

Note: 1 Pekin, the presumed layer, has a much lighter almost yellow bill and is now white, whereas her sister has a darker orange bill with yellowy cream colored feathers, indicating that she has more xanthophylls are being excreted in her egg yolks, and therefore has begun laying. Seems odd for the other Pekin to not have started laying yet at 7 months old and while it is a bit early for the Blue Swedes, perhaps one has layed a few smaller eggs?

 

[Rickba]

Hi young lady, There is no certain size of eggs. One bird will lay eggs of varying sizes and shades throughout her laying lifetime. My birds do the same things.

 

[aart]

I know with chickens you can get slight varied sizes, especially when they first start laying. That big one could be a double yolk.
Not sure if you can check ducks pelvic points,
to see who is laying and who is not like you can with chickens.