Intel Mac上で日付オブジェクトを読み出すと日付が狂う、という件についてUSのAS Studio MLでPaul Berkowitzがこんな説明をしています。Panther->Tigerだからではなく、PPC Mac-> Intel Macだから問題が出たのでは?
Date objects are actually stored by AppleScript as (long) integers
representing the number of seconds since Jan 1, 1904. The limit is
equivalent to some time on Feb 5 or 6, 2039, if I remember correctly. (It's
2^29 or 2^31 something like that.) Larger numbers start again at 1/1/1904,
negative numbers backwards from 2/2039. So your "wrong date" represents 0:
it could be an "invalid" number on the wrong CPU defaulting to 0. There's
probably supposed to be some coercion that isn't working. I believe dates
work OK in regular AppleScript .scpt and .app files made in Script Editor
and ported to the other architecture. It could well be some
Cocoa-to-AppleScript translation that's going wrong here.