Do hens lay small eggs after taking a break or molting?

The reason I ask is because my hens have been slacking off lately, however I have two new girls hatched late June. Last week I found a small white egg and today a small darker brown egg (like my RIR lays). My two new girls were both suppose to be cuckoo marans, however one is clearly not. I think she is a Plymouth Rock, although she is slightly bigger than my 18 month old BR's. Neither small egg is the color I am expecting to get from the Maran. I will be so disappointed if neither girl give me a dark brown egg. My new girls are about 21 weeks. Your opinion is most welcome. My others girls consist of BO's, RIR, Calf. White, EE's and BR's. Thanks!