E is the batch number, and is one of the first, or maybe even the first batch od The Irishman Single Malt. Batches seen in the first couple of years of release include batches E,F,G,H,M. AD is a much later batch.
E1414 bottle is coded L6, The AD bottle is not mine so can't comment on it. I know that the E coded bottles are the first batch. Just wondered what the E code actually stood for.
I've no idea as to the origin of the batch system either and whether E was the first but as thewhiskeybro says I too believe it was the first release.
I have E1705 which I purchased at the time of release. They originally were released in batches of a maximum of 6000 a time I believe but that may have changed since.
I also have the Irishman superior which is the blend and then changed to the Irishman 70 and now the Irishman Founders Reserve.
Not sure what type of blend it was originally but it is now a blend of PPS and Malt so nopt aa grain blend as we're used to. And similar to their other creation the wonderful Writers Tears.