At the 10:30 Sunday mass, like at any other parish, there is a process of gifts from the back of the Church to the altar. At this particular mass there are too many attendees to bring up all the hosts to be consecrated at once. It would be possible but would require multiple pattens and would be awkward to carry. (An excellent problem to have, if you must have one.) For the sake of the symbolism of the bread and wine to be consecrated being brought up by the people it isn't necessary that all the elements to be consecrated are brought up in procession. It's okay that about 200 hosts in a separate patten and 8 pre-filled chalices are kept in the sacristy behind that altar. Only some of the hosts and the little bit of wine needed to fill the priest's chalice is brought forward with the gifts. A portion can symbolize the whole lot.
This past Sunday we forgot to bring the extra hosts from the sacristy out to the altar. It wasn't until after the consecration that we realized we had forgotten to bring them out. There was the one patten full of unconsecrated hosts sitting there on the sacristy table.
One might be tempted to just bring these hosts out and mix them in as if they hadn't been forgotten, but, that would be the absolute wrong thing to do! I emphasized the symbolism of that carrying down of the gifts and it's inherent flexibility in order to contrast it with the inflexibility here.
These hosts that were left in the sacristy are not interchangeable with those that made it out to the altar because the Consecration that the priest does at the altar is not a symbolic act. It is a real act. The bread and wine that were on the altar literally have become the Body and Blood of Christ, the Eucharist (the physical properties, the "accidents" in philosophy-talk, remain of bread and wine but their nature is no longer so simple. They have been transubstantiated.) To mix these unconsecrated hosts in with the consecrated ones would be to terribly mislead the faithful. (For the record, no one present was suggesting we do so.)
This wasn't a big deal, of course. We just left them where they were in the sacristy. It would be ideal to have consecrated them so that there would be enough for everyone to have a whole host but in this case those distributing communion just broke the ones that were consecrated into smaller pieces so that there were enough for all present (no matter how the small the piece the True presence of the Body of Christ is not diminished) At the end of the mass it was probably entirely forgotten, except hopefully by the servers but I choose to share it as an illustration of the seriousness of the Eucharist. It's not just a symbol. It's a reality that can't be fudged.