Those preserved specimens in natural history collections didn't get into their jars or drawers on their own. Quite a bit of work was involved, not only in the field, but also in the lab. This time lapse video from the Ichthyology Collection shows one of the first steps, sorting the specimens into jars.
And then what happens with all these shiny new jars? The work doesn't stop there! A different staff member typically performs a more careful ID verification. Fish are often hard to identify and require counting fin rays or scales and sometimes dissections or x-rays are required. Once identified, the specimens will be counted and the smallest and largest will be measured. After all the data are together, they are catalogued in the database. Formal permanent labels will be inserted where they will live inside the jars with the fish. After topping the jars with more 70% ethanol, they will be shelved in permanent climate-controlled storage and made available for researchers to examine indefinitely, potentially persisting for hundreds of years!