On a shot where you your colored balls are still on the table, you cannot call the eight ball.
3.6 Shots Required to Be Called
The eight ball may be called only after the shot on which the shooter’s group has been cleared from the table.
So on the shot you've described, the eight ball could not have been legally called. In that case, ...
From WPA rules, the general rule for all types of called shot games contains:
1.6 Standard Call Shot
In games in which the shooter is required to call shots, the intended ball and pocket must be
indicated for each shot if they are not obvious. Details of the shot, such as cushions struck or
other balls contacted or pocketed are irrelevant.