Given the relevance to OCaml, I wonder if it's worth taking this opportunity to add a lint warning (or even error) when the exception and licence combination is invalid (cf. ocaml/opam-repository#19010 (comment)).

opam-repository features these uses of OCaml-LGPL-linking-exception:
LGPL-2.0-only WITH OCaml-LGPL-linking-exception
LGPL-2.1-only WITH OCaml-LGPL-linking-exception
LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception
LGPL-2.1 WITH OCaml-LGPL-linking-exception
LGPL-3.0-only WITH OCaml-LGPL-linking-exception
LGPL-3.0-or-later WITH OCaml-LGPL-linking-exception

The exception has existed with both GNU Library GPL v2.0 and GNU Lesser GPL v2.1 (clause 2 is identical in both and, although I'm not lawyer, clause 6 does not look materially different), so I think the LPGL-2.0-only, LGPL-2.1-only and LGPL 2.1 uses are clearly valid.

With even more emphasis on not being a lawyer, I would assume that LGPL-2.1-or-later requires a legal common-sense application of the exception to LPGL 3.0 (i.e. the fact that the clause numberings are different does not invalidate the intent of the exception).

However, that's quite clearly not the case for LGPL-3.0-only and LGPL-3.0-or-later so it would be a good service to the community if we rejected them!

Superseded by #4768. Thanks though!