What is the difference in meaning between these two phrases?
not as effective as it could have been
not as effective as it could be
not as effective as it could have been
This is referring to an event that occurred in the past. An event happened and its effectiveness was sup-par. For example:
Napoleon's efforts at Waterloo were not as effective as they could have been.
As for your other phrase:
not as effective as it could be
This contains the possibility of future effectiveness. A demonstration of the effectiveness has obviously been conducted, and the speaker has decided that improvements in the process could be made so that it is more effective in the future. For example:
The bug spray isn't as effective as it could be. I'm sure the research lab can make it kill bugs more quickly.
"... could have been"
instead of ... could be
or other way around - should have said " ... could be"
but actually said "... could have been"
?