My answer is that GIB don't really play LGST.
After 2♠ cuebid to show limited raise or better,I can't bid up to game directly due to minimum hand,so I need to have LSGT,and then rebid 3♣,surprisedly GIB don't bid 4♠ instead of 3♦ as a reverse invitational,I held small tripleton,I only bid 3♥,what else? And another problem is 3♦ was alerted as 3+♦,actually it is doubleton.