There are conflicting version numbers in DTrace. For example,

libdtrace/dt_open.c
const dt_version_t _dtrace_versions[] = {
[...]
DT_VERS_1_6_3, /* D API 1.6.3 /
DT_VERS_1_6_4, / D API 1.6.4 /
DT_VERS_2_0, / D API 2.0 */
0
};

libdtrace/dt_version.h
* You must update DT_VERS_LATEST and DT_VERS_STRING when adding a new version,
* and then add the new version to the _dtrace_versions[] array declared in
* dt_open.c..
[...]

 #define DT_VERS_1_6_4 DT_VERSION_NUMBER(1, 6, 4)
 #define DT_VERS_2_0 DT_VERSION_NUMBER(2, 0, 0)
 #define DT_VERS_2_0_1 DT_VERSION_NUMBER(2, 0, 1)
 #define DT_VERS_LATEST DT_VERS_2_0_1
 #define DT_VERS_STRING "Oracle D 2.0"

dtrace.spec

 Version: 2.0.2

GNUmakefile

 VERSION := 2.0.1

One issue is that there is a sense of "API" version in the code base, but that is then also immediately ignored and handled as a DTrace version instead. That probably resulted from having no other real libdtrace consumer other than dtrace itself, so having a well specified (and versioned) API has not been of much interest.