Thanks in advance for some clues on the below:

Has there ever been a release of LMDB that adds/removes/changes API?

On both Debian 10 (with lmdb 0.9.22) and Debian 11 (with lmdb 0.9.24) , under lib/ I see

liblmdb.so -> liblmdb.so.0 (symlink)
liblmdb.so.0 -> liblmdb.so.0.0.0 (symlink)
liblmdb.so.0.0.0 (the original file)

Has this always been at 0.0.0 since the beginning of LMDB? From the point of view of what the LMDB developers would expect, I mean. (I have no idea which distros were distributing LMDB in the early days)

What are your intentions regarding this .so versioning in relation to adding/removing/changes to the API?
Something like this, perhaps? https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html

Another Linux distribution (NixOS 22.11, with lmdb 0.9.29) has *only* this under lib/:

liblmdb.so (the original file)

Does this sound right to you?
What I mean is, when people compile LMDB down to an .so, would you expect them to normally add a version after the ".so"? (As they apparently did in Debian)