Build id vs Version number in Synaptic

[Jim]

Why do some packages use a build id to show the latest version and 
others seem to use a version number?  For example Libreoffice Calc shows 
a build id while Firefox shows a version number.

This sometimes makes it difficult to determine how current a package in 
a repository is when comparing it to a version of a program you may have 
seen on the net.

Regards,  Jim