I received my I-797A extension in just 4 weeks, what's wrong?

[lcolorado]

I submitted a TN visa extension request using an I-129, and received the approval in just three weeks. However, the status online on the USCIS site say "Received," not approved.

The processing time posted for the Vermont office is 2 to 4 months.

I don't know if I should do the happy dance, or I should worry. Has anybody seen anything like that?

Is this a USCIS mistake? Is there a chance that they could retract the approval?

Thank you,

Luis