Hi Jim,
No cyphers in Arabic script are known to have been used in Europe before the early 1400's, so please forget about the theory that it might be that old.
If you are interested in the shape and form of 15th c. Gothic crossbows, please see my thread
http://www.vikingsword.com/vb/showthread.php?t=7516
You will at once see the differences.
And: I cannot remember seeing any other trap crossbows at the moment, they seem to be quite rare indeed.
Best,
Michael