https://bugs.openldap.org/show_bug.cgi?id=9700
--- Comment #1 from Ryan Tandy ryan@openldap.org --- https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.... https://autotools.io/libtool/version.html
Using -release versioning was added in 2.2, commit f1f1b0f69b560aca08745e3e01faddb3321fd264. For returning to the other style, I would expect the library would resume where it left off, also taking into account any ABI changes that happened in the interim.
The last release without -release was 2.1.30, the version-info was 2:130:0. Is this just built from the version string? 2:600:0 I guess is a technically correct libtool version (if unnecessarily large) *IF* libldap 2.6.0 is ABI-compatible with 2.1.30... This also assumes there will never be an ABI change before 3.0.0.
0:0:0 is probably still appropriate for master at all times.