FYI, in fact this confusion comes from a bug introduced a long time ago:
Initially, the field name was "Sheet" not "Datasheet".
It should be "SchematicSheet"
The purpose was to be able to create a component acting as a hierarchical sheet:
The component in a root sheet, and its internal sheet ("SchematicSheet") similar to a sub sheet.
But unfortunately, it was never done, and one day the word "Sheet" became "Datasheet", thus creating
a serious confusion.
Perhaps the "DATASHEET" field (attached to the symbol) and the "documentation" string (attached to a
alias) should be clearly redefined for the V5.
By the way, do you know why the .dcm file exists?
It is similar to the .idx index file of old spice libs.
In the early time of eeschema, Kicad was stored on a server and was used in classrooms and on PCs
connected by a "slow" network link: network cards were ISA cards and the link speed was roughly 2400
bps.
So loading all needed schematic libraries to choose a symbol was a too time costly process, making
Eeschema barely usable.
Using small .dcm files to display a list of symbols and some info fixed this issue.
Nowadays, link speed, PC speed and memory sizes have 3 order of magnitude, and .dcm files (a relic
of this time) is more an annoying feature.
