Currently media-sound/pulseaudio has some USE=gdbm conditional license on it, GPL-2 if enabled, LGPL-2.1 otherwise.
The question is if we really need to be expressing this in LICENSE manually, or it could be simply LGPL-2.1+ and any incompatibilities would be implicit.
If not, then I'd have to update it to be actually correct in these terms, which would make it be something like
LICENSE="!gdbm? ( !lirc? ( !equalizer? ( LGPL-2.1+ ) ) ) lirc? ( !gdbm? ( GPL-2+ ) ) equalizer? ( AGPL-3+ !gdbm? ( GPL-2+ ) ) gdbm? ( GPL-3+ )"
instead of simply
LICENSE="LGPL-2.1+ equalizer? ( AGPL-3+ )"
as-is due to gdbm moving away from GPL-2+ to GPL-3+ is wrong too, but I'd rather fix it up as needed fully. gdbm package license is probably wrong too (GPL-3 only right now, but likely GPL-3+ really).
This used to have to be even more convoluted to be correct with linkage considered due to libsamplerate being GPL-2 (possibly not "or later", meaning even incompatibilities), but it got relicensed to 2-clause BSD and I've asked that version to be stabilized now to avoid that mess (and using that 2-clause BSD should simply change it to LGPL or GPL or something).