Can you be "overtrained" going to failure if your lifts continue to go up or in all probability they should decrease if you are correct?
If you're not making
optimal progress, you are overtraining. You don't have to experience a decrease in strength in order to be overtraining. Overtraining simply means "training too frequently and/or with too much volume." If your intensity is high enough to stimulate growth, yet you're not progressing at an absolute maximum rate, you're overtraining to some degree, even if you're progressing a little.
In other words, it's actually impossible to tell whether or not you're overtraining unless your strength is actually decreasing. Who knows, you may go lift and gain 5 lbs. on each lift. BUT, maybe you
could have added 10 lbs to each lift
and gotten a couple extra couple reps on top of that with a bit less volume and another rest day. It's guesswork based on expectations, but what you
can do just keep striving for what you consider to be optimal progress for you. Just don't do too much work during your workout or train too often. That will cause overtraining.
But yeah,
if intensity is high enough to stimulate growth, yet you're not making
optimal progress, you are overtraining to
some degree because your training is not
optimal.