Black dominant (KK): CC EE BB DD gg intmintm 
Yellow (ee): CC KK BB DD gg intmintm 
Chocolate (bb): CC EE KK DD gg intmintm 
Black carrying chocolate (Bb): CC EE KK DD gg intmintm 
Black carrying chocolate and yellow (Bb Ee): CC KK DD gg intmintm 
Black carrying yellow (Ee BB): CC KK DD gg intmintm 
Yellow carrying chocolate (yellow liver) (ee bb):  CC KK DD gg intmintm 
Dominant black carrying brindle (Kkbr): CC DD gg intmintm 
Chocolate carrying brindle (kbrkbr bb): CC EE DD gg intmintm 
Yellow carrying brindle (ee kbrkbr): CC BB DD gg intmintm 
 

In our database I found 480 unregistered Labrador retrievers, born in the U.K. between 1897 and 1962.  
Further more I found 21 interbred or fullbred Flatcoats or Chesapeake Bay retrievers in our Labrador retriever database, all born in the U.K. between 1914 and 1933.  
It is well known that even in the 1980s Golden retrievers were used to improve the coats of yellow Labradors, and we also know that the Kennel Club hasn't been informed about these interbreedings. 

There are a lot of missing links in our database, and sometimes the reasons for this are rather obvious. Of all the 21 interbred or fullbred Flatcoats or Chesapeake Bay retrievers, most of them being Field Trial champions, we could only track the ancestors for more than two generations of two dogs. The information about the ancestors of the other 19 interbred dogs was simply removed from the files in the 1930s. It seems that some well known Labrador breeders didn't want the public to know that their succesful dogs were partly the offspring of interbred dogs.  

Two well known Chesapeake Bay retrievers were a dog called Jolly, who sired the male Labrador retriever Jolly Sam, born before 1933, and the bitch Corydalys, who was the dam of the female Labrador retriever Micklefield Juno, born before 1925. 

 
Chesapeake Bay retriever 

 
Male champion Chesapeake Bay retriever 

 
Three male Chesapeake Bay retrievers 

 
Old female Chesapeake Bay retriever 

Some of us who are breeders of Labrador retrievers won't find any difficulties to recognise characteristics of the Chessies above in many of our chocolate Labs.  

 
Flatcoat retrievers 

Given the depletion of breeding stock, especially after the second World War, Flatcoats and Labradors were widely interbred to broaden the gene pool and increase the number of dogs to a safer level. For example, the Labrador CH. Horton Max, a well-regarded Labrador at the turn of the century was actually an interbred, sired by the influential CH. Darenth, a Flatcoat, while Horton Max's son Maxim's dam Horton Flo was also an interbred; her sire was the Flatcoat  Horton Viceroy, born before 1912. For some reason, while those breeders in Flatcoats are aware of this mixing, many Labrador breeders are not. 

Another famous Flatcoat who influenced the Labrador retriever was the bitch Stoneleigh Quality. She and the Labrador Brayton Swift were the parents of the Labrador bitch Fairgirth Bell, born before 1917.  

Despite the widespread removal of the descendants of interbred dogs from the database, are we still able to track some of them down? Yes we are. 

At the very bottom of this 6-generation pedigree of the famous Holton Baron, we find a black bitch called Kwa. She was born before 1933.  
Now let's take a look at Kwa's pedigree:  

The blood of the interbred Stourhead Gilda, born before 1924, can be found in many American lines.  

So Labrador breeders have nothing to be ashamed of. They did well. When I look at my labs, blacks, yellows and chocs, I'm sure I see some characteristics of Flatcoats, Goldens and Chessies. And all I can do is thank the breeders who had the wisdom to cross these breeds into their lines.