
If they are done by NDTR then they would be either Letter (denoting region), Number (denoting a grouping, GSD, Hound etc), another letter, (denoting the identity of the tattooist), followed by the individual number, so all my puppies are R7K???, those done as adults would be RK???.
As has been said they are usually tattooed in the right ear, but can be done in left say if there was a reason not do do the right, or a redo if the previous tat was bad.
As it is Southern Ireland it is worth finding out if there are any other Registries (outside Greyhounds, hunting hound packs) that tattoo over there.