I have myself never heard of this, and never had anyone asked me when I was a historical clerk and was the one taking the attendance count, to count only those who had participated in the ordinance of the sacrament. And that was in the 80s and I had never heard of anything nor found anything written then, before then, or up until now, about any such practice of counting only those that participated in the ordinance having happened. With an occasional very rare exception caused by unrelated factors, it's always the total number that were in the meeting that are counted.
Given that the count usually includes any nonmembers that may be attending, and some may take the sacrament (this is noted in the Aaronic Priesthood section of Handbook 2), other nonmembers may not although the Handbook says they may if they desire to, so counting only those who took the sacrament is an inaccurate way to get the count for purposes of counting those who attended sacrament meeting.
In fact, I've heard that in a few places, sacrament meeting attendance has been over 100 percent due to the number of nonmembers attending, and the high activity and retention of new members in those few areas where this is happening.