I think 2.2 million is a fudge. There have been many leave who still remain on the books. A couple years ago, we needed our son's baptismal certificate, so called the church we used to attend to get a copy. We were still on the books as members although listed as inactive. Inactive membership is included in the membership count we were told. BTW...we left 18 years ago, so we were very long term inactive. ;) I asked them to just remove us as we had left the church.
I agree with you that their numbers are a "fudge". It used to be that the parish rector was required by canon law to purge the parish rolls every year or at least every three years. Communicants were also required to attend, at a minimum, three Sundays each year or they could be dropped from the parish rolls.
Like you, I removed myself from the Episcopal Church. A few years later, I learned that I had not been dropped from my former parish's roll. I knew of a number of others who were still being counted on the parish roll. This is quite common throughout TEC.
I'd wager that the Episcopal Church probably has about 1.2 to 1.5 million "baptized" members and probably less "Confirmed" members.