If they look partridge, does that mean they have the Eb or e+ base? I don't know which hens laid which eggs so I don't know if they came from Heartland or not. My 2 roosters did. Most of my hens did but 3 of them did not, so I don't know their histories or even how to find out about them. If I could be sure about the mothers coming from Heartland, I could ask Alan but then again, he may not know.
In general yes, the “Chipmunk” like patterning on chick down(fluff) feathers shows that the bird is on an Eb or e+ base, although it may be split on that base and have any other patterns mixed in. I can show you a huge variety of chick down feathers that can be created through various combinations with partridge, I did a lot of test breeding to try and figure out what genes my birds were carrying and learnt a lot in the process.
As with a lot of things related to chickens, it is difficult to predict a hard and fast rule. For example me saying that the eye stripe is definitive is because it is for me and my birds, because I know what genes my birds are carrying. But that did involve hatching over 100 chicks from test breeding and breeding back to the parents.
A lot of the birds I hatched looked partridge when they were very young. And that is a sign of the base genes I was talking about earlier. They grew up into all sorts of variations on partridge though. So it isn’t a hard and fast prediction that you will have a flawless partridge. Only time will tell that.
Partridge birds look best after first or even second moult between 12 months to a 24 months. So it is a difficult variety to breed(like a lot of patterned varieties), because as breeders we have to keep them a lot longer than a black or white to see if they have potential.
Sorry I got carried away there, if they come out looking like little Chipmunks, then they will be on either of the two bases mentioned, which means the parents will carry those genes even if they do not display them on the outside. To really see what they are carrying, you could keep males and females that hatch and look like partridge and breed them back together, that will show you for sure which genes are causing that look.
Hope that helps.
Andy