The default display name, if nothing is provided by the extension, is the file name.
The display name could be changed in different versions. There are three versions
of change1.oxt available:

v1: no display name
v2: change1 de
v3: change1 de - changed display name -

change1_mod.oxt is the same as change1.oxt version 1 except that is has a display name.
This situation should actually never arise, because the version should always be 
changed when the extension is changed - and be it only the display name.