This means that the number associated with the entry for Husemoller will be larger than the number for Auberteau. LaTeX will not resort this list for you. You need to be aware not produce an unsequential listing. To be used by LaTeX, the bib file must be processed to produce a bbl file. This is done with the bibtex command.
Several options are available besides plain style.
A comparison of several bst files is available along with the dvi files. The examples were generated using the script Embib which takes the entries in the file pat.bib and creates a latex file pat.tex and the file patnocite.tex. The script then runs latex, bibtex and then latex to produce the file pat.dvi. The bst file oplist.bst allows an entry for cataloguing the files. In order for the bst file to be found, it should be on a path where LaTeX expects input to be found.