Looking at an example of routing calls to PRI first then FXO I found the following:
dial-peer voice 1000 pots
destination pattern 91..........
dial-peer voice 1001 pots
I thought the digits that matched the destination pattern were stripped when forwarded to the PSTN. In this example it seems that the "1" would not be sent to the PSTN and the call would fail. Also why does the PRI need the "forward-digits" command the the FXO doesn't?