I've just set up a project using the DF1 protocol and I can validate with no errors using either addressing syntax.
FYI, when I look at the properties of the DF1 driver here's what I see:
In the project navigator, expand "PLC Access Drivers" then expand "View Native Drivers", then click on "AB DF1". Under "Configuration" I see "DF1 -C2 -B19200 -PN -R1 -T1000".
Then when I click on "Device1" (the name assigned to the specific instance of the DF1 protocol) I see "-PSLC500 -R0 -S0 -B0 -L1 -G0".
When I look at the properties of my Boolean tag in the variables list, under "Data Source" I see "PLC Access" and under "Device" I see "Device1".