Tom,
You and me both!. There is an old post still active that involved Denny R and an AXT in his collection that had, what was thought to be an SMF crossguard. However I believe by the end of the discussion it was agreed that there were enough differences for it to be attributed unique.
I was hoping for a couple of close ups to write off hand enhancing as a possibility for the variation or if it was possibly a modified base crossguard from an early Alcoso or Holler.
I have comparison pictures to post but I need to get the owners permission prior to uploading.