The current implementation of extract-messages.sh does not support extracting of pot files dedicated for a specific major version.

A related support could be easily added by specifing two additional get text wrapper, which could be used in Messages.sh.

See the following example:

Say we have a major version A and B there should be in version A extract-messages.sh  the following code fragment:

    if test -f Messages.sh; then
        # Note: Messages.sh is supposed to get the translators' placeholder by rc.cpp
       enpodir=$enpodir \
       podir=$podir \
       srcdir=. \
       XGETTEXT_PROGRAM="${XGETTEXT:-xgettext}" \
       XGETTEXT_WWW="${XGETTEXT:-xgettext} $XGETTEXT_FLAGS_WWW" \
       XGETTEXT="kde_xgettext" \
       XGETTEXT_A="kde_xgettext" \
       XGETTEXT_B="true" \
       PACKAGE=$PACKAGE \
       bash Messages.sh
   fi

and in version B 

    if test -f Messages.sh; then
        # Note: Messages.sh is supposed to get the translators' placeholder by rc.cpp
       enpodir=$enpodir \
       podir=$podir \
       srcdir=. \
       XGETTEXT_PROGRAM="${XGETTEXT:-xgettext}" \
       XGETTEXT_WWW="${XGETTEXT:-xgettext} $XGETTEXT_FLAGS_WWW" \
       XGETTEXT="kde_xgettext" \
       XGETTEXT_B="kde_xgettext" \
       XGETTEXT_A="true" \
       PACKAGE=$PACKAGE \
       bash Messages.sh
   fi

In a Message.sh file intended for version A there should be used 

#!/bin/sh
$EXTRACTRC `find . -name \*.rc -o -name \*.ui -o -name \*.kcfg` >> rc.cpp
$XGETTEXT_A `find . -name \*.cc -o -name \*.cpp -o -name \*.h -name \*.qml` -o $podir/my_version_a.pot
rm rc.cpp

in a Messages.sh file indented for version B 

#!/bin/sh
$EXTRACTRC `find . -name \*.rc -o -name \*.ui -o -name \*.kcfg` >> rc.cpp
$XGETTEXT_B `find . -name \*.cc -o -name \*.cpp -o -name \*.h -name \*.qml` -o $podir/my_version_b.pot
rm rc.cpp

and in a Messages.sh file indented for version A and B 

#!/bin/sh
$EXTRACTRC `find . -name \*.rc -o -name \*.ui -o -name \*.kcfg` >> rc.cpp
$XGETTEXT `find . -name \*.cc -o -name \*.cpp -o -name \*.h -name \*.qml` -o $podir/my_version_a_and_b.pot
rm rc.cpp

In the case where a Messages.sh is called for an unsupported major version the gettext related command line is expanded to 

true `find . -name \*.cc -o -name \*.cpp -o -name \*.h -name \*.qml` -o $podir/my_version_b.pot

and is ignored.