The issue may be that "LiveCycle Designer ES defines day one for the epoch for all date functions as Jan 1, 1900".
The website you referred to has the following statement "Epoch has a few meanings (see also http://dictionary.reference.com/search?q=epoch). The definition that we'll use is "0" in computer time. While there are folks who will argue this, for our purposes, this "0" time on our calendar was January 1, 1970 00:00:00 GMT"
That would explain why the answer is approximately 70 years off!!
I think I will use your script (thanks!), but truncate the answer to the last 8 digits.