There is Mass at Yankee Stadium today, hundreds of priests concelebrating, thousands of laypeople. The Pope has expressed his doubts about such events, saying he did not think that this is what Christ intended.
The words of consecration begin "Hoc est..." not "Illud est...", "This is..." not "That is...". There is an intimacy between Christ and the elements, "he took bread into his holy and venerable hands", as the Roman Canon says. Is one really saying Mass if one can't see, let alone touch the elements?
Before the introduction of concelebration, there was hardly any theological discussion of it. There were mutterings that the Byzantines had always done it, that it had been done in the west at ordinations, but no-one had actually asked WHAT was being done. The parallel seems to be the consecration of the chrism, at the Chrism Mass in Holy Week, the bishop prays and the priests "associate" themselves with this action by holding out their hands, in the epiklesis gesture but the priest does not co-consecrate.
Are a thousand priests saying Mass in the Yankee Stadium doing the same as a thousand priests at their own altar, as the Code of Canon Law says a priest may offer Mass for a particular intention at these Masses, and take a stipend, it, at least makes this is the presumption, but canon lawyers ain't theologians!
Maybe the Ball Park Mass and todays might get the Petrine brain cells going on this matter.