The pattern I use is similar to the one you were using, modified for the reasons you are doing so (duplication), as well as being an indication of which litter of a given set of parents, an indication of sex, and ranking of the bunnies in a litter.
The tattoos are: (litter number if it's the second or more litter from the same parents)(sire's initial)(dam's initial)(kit number, males being odd numbers, females even numbers, and going from best to least good).
So, the first litter from Girdwood and Kitty would be GK1 (buck), GK2 (doe), GK3 (buck), GK4 (doe), etc. Their second litter would be 2GK1 (buck), 2GK2 (doe), etc.
If I have rabbits of the same sex with the same initial, for instance Surprise, Starlight, and Stardust, I add a second letter to their initial when the second one comes up, e.g. Surprise = SU, Starlight = ST, Stardust = SD. So Girdwood and Surprise's second litter would be 2GSU1 (doe), 2GCU2 (doe) etc.
If you add your rabbitry initials SB, you'll get a maximum of eight characters with this system, or rarely nine if the doe has more than 5 of one sex in a litter. If Surprise (SU) had six female kits in her second litter with Kibble (KB), you might end up with SB2KBSU2, SB2KBSU4, SB2KBSU6, SB2KBSU8, SB2KBSU0 and SB2KBSU12. I don't usually tattoo butcher growouts, though, so I've never had to use the maximum number of digits in my system (which is seven since I don't use a rabbitry indicator).
I've found that it's really helpful to know the rabbit's parentage by the ear number; I don't have hundreds of rabbits to keep track of, but it's funny how even with just a dozen or two rabbits, that stuff can blur in your memory when you're thinking about culling or breeding pairs. Adding the birth year is pretty handy too, but I find the parentage more useful and like to keep the tattoos as short as possible. It's also been very interesting to see how my judgment (of which rabbit is best at tattoo age, which is usually between 6-12 weeks) changes over time - I used to end up with a lot more GSU
6s with Grand Championships than I do now (when they're usually the 1s and 2s), so I think the exercise has helped refine my assessment abilities over the years. (I also have the occasional buck ending in an even number, but that's more amusing than important.
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