Here is my guess:
The site illflem posted was dated March 4, 2001. What I'm thinking is the XLA is a "newer" additive and at the time it was introduced into the oil, they labeled the bottles as such. Now I'm guessing that the XLA is still in there they just no loner label the bottles.
Here is a number I found for Shell Lubricants, you might try to give them a call.
1-800-64-LUBES