Hi,
The LF is an ultra-low power derivative (maybe just selected from the normal production line) and, as you say, is rated only up to about 3 volts. Since the PICaxe 08M2 is rated for use up to around 5 volts, I think we can assume that it employs the 12F1840 chip (i.e. the "grey" table cells in the data sheet).
Cheers, Alan.