Why your eyes and memory will let you down
A flock of twelve hens of the same breed is twelve variations on one bird, and the differences you swear you know in June — the slightly paler one, the bold one — dissolve by October, especially after a moult shuffles everyone's plumage. That would not matter if records did not matter, but they do: which hen has stopped laying, which one was treated last month, which bird is the persistent egg-eater and which is the flock's grandmother who should be retired from the breeding pen. Every one of those records is worthless, and occasionally worse than worthless, if it is attached to the wrong chicken. Identification has to be physical, not remembered.
Leg bands are the flock standard for a reason
Fit each bird with a leg band — spirals for growing birds, flat numbered bands for adults — sized so it slides freely on the leg without slipping over the foot or squeezing the skin. Band pullets as they approach lay, when you are handling them anyway, and write the number down on the spot, because "the blue band, I think number seven" is how records rot. In a bigger flock, run a two-part system: colour for the hatch year, number for the individual, so a glance tells you a bird's age group and her record tells you the rest. Check band fit whenever you handle the birds, and check growing youngsters often, because a band that was loose in spring can cut in by autumn.
Take photographs that would actually settle an argument
At banding, photograph each hen twice: a full side profile showing her shape, carriage and plumage pattern, and a closer shot of her head showing comb size and shape, wattles and eye colour. A photo that could not distinguish her from her sister is decoration, not identification. Name or file the pictures by band number rather than by the bird's pet name, and retake them after each moult, when feather patterns shift and last year's portrait stops resembling this year's hen. Keep the photos with the record they belong to, not scattered through a phone camera roll of two thousand images.
Record the natural markers as a cross-check
Bands come off, so give every bird a second identity in words. Note comb shape and any flop or extra points, eye and leg colour, odd feathers — the white-tipped tail, the speckled hackle — plus fixed quirks like a crooked toe, a healed spur or a missing toenail. Add temperament while you are at it: first to the feeder, flighty, broody every spring. These notes are what let you re-identify a bird who has lost her band in the bedding, and they catch the embarrassing error where two hens swap identities in your records because their bands were misread in poor light.
When a band comes off, fix it the same day
A bandless hen in a look-alike flock starts becoming anonymous within days. If the bird matters — she is mid-record, being watched, or part of a breeding group — catch her, check her against the photographs and marker notes, mark her temporarily with a dab of animal-safe marker spray, and re-band her before she goes back. Her KinsLe Pet Pass entry is where all of this lives together: band number and colour, portrait photos, natural markers and notes, so the identity you built for her can be shown to anyone helping with the flock and never has to be reconstructed from memory again.