I can't find the reservations I received prior to going live with the channel manager

The channel manager will only display reservations made through your connected Booking Sites only after you go live with that site.

If any reservations that were created prior to the new connection are cancelled or amended, they may failover to email as the original reservation will not be located within your PMS and therefore cannot be updated.

For Booking.com, we are now able to perform an import of all future reservations.  These will not be delivered to your PMS but will be stored in the channel manager for reference.