Interestingly, the phrase, "delayed deadball" did not originate in professional baseball. There was no need for it.
Schools, at least the Academy, and PBUC, do not teach or label positions as ABC for what they perceive to be good reason.
At first, many believed, and later confirmed, that labeling these positions so exactly would lead to umpires picking exact spots on the field and "get married to them" disregarding all factors but the base(S) that had runners and simple geography. Many amateur trainers will even march out on the field, point to a spot and and say, "THIS is "B".
The pros prefer to emphasize that positioning is dependent on many factors and no one spot is the best for a single runner on first. Thus, in training, they refer to the base umpire being on the grass to the first base side of the mound and about half way between the rubber and second base. This provides a lot of area for the umpire to select a spot given what he has observed about the pitcher, the runner, the fielder, and the game situation.
Again, as with the amateur misnomer of a delayed deadball, this goes beyond semantics and addresses practice and results.
I went to school to rid myself of old habits and to become the best umpire I could be. I was too old to hope for a contract. It was, by far, the best decision I've made regarding umpiring.
I believe with the increased number of amateur umpires attending schools and professional camps, and bringing their training back home, combined with FED's demonstrated indifference to quality of training, the standard will become pro mechanics and pro philosophy.