bsd.licenses.mk: where is "or any later version" construct?

[Anonymous]

One of my ports have this in its source header

 * GNU LGPL information
 * --------------------
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

Looking at bsd.licenses.db.mk it does have LGPL21. However, it doesn't
match in a sense that user can apply any later version. Here is a quote
from FSF site

  13. The Free Software Foundation may publish revised and/or new versions
  of the Lesser General Public License from time to time. Such new
  versions will be similar in spirit to the present version, but may
  differ in detail to address new problems or concerns.

  Each version is given a distinguishing version number. If the Library
  specifies a version number of this License which applies to it and "any
  later version", you have the option of following the terms and
  conditions either of that version or of any later version published by
  the Free Software Foundation. If the Library does not specify a license
  version number, you may choose any version ever published by the Free
  Software Foundation. 

IANAL, but I think LGPL3 is applicable here, too. So, I've tried to set

  LICENSE= LGPL21+

but it doesn't work. I've figured this will work

  LICENSE= LGPL21 LGPL3
  LICENSE_COMB= dual

Is this correct usage or I'm missing smth?