Rather that using the extenable command I added a route-map that matched the input interface. Does that meet the task objectives too? It seems to provide the same results
ip nat inside source static 136.1.128.9 136.1.19.250 route-map VLAN19_IN
ip nat inside source static 136.1.128.9 136.1.99.250 route-map VLAN123_IN
route-map VLAN19_IN permit 10
match interface GigabitEthernet0/0
route-map VLAN123_IN permit 10
match interface GigabitEthernet0/1.123