Nothing could separate the Baggies and the Lions at The Hawthorns on a tight and tense afternoon where a draw was a fair outcome.
Albion were the better side before the break and created useful openings but allowed their visitors to come back into the clash in the second half.
The hosts moved a place to ninth with a point but remain five points from the top six - even though rivals above them lost on an afternoon that will go down as a missed opportunity.
One of the contentious moments from an Albion attacking perspective came four minutes from time, where substitute Daryl Dike was brought down in the box by Millwall goalkeeper George Long. It was a clear foul but referee Simpson went along with his assistant's incorrect offside call - incorrect as the ball had gone through off a Millwall leg.
Corberan, though, accepted that wrong decisions can happen, however was more incensed by an even later incident in which Dike was kicked to the ground, seemingly inside the box while Brandon Thomas-Asante attacked.
"I watched this action back. Unfortunately, the referee didn't make the right decision," Corberan said. "There were two actions, but maybe he saw another one which wasn't beneficial for us. To be a referee in these types of games is very, very complicated.
"Sometimes with VAR they have trouble making the right decisions, but it's true that if you analyse the actions of Okay (Yokuslu, who was tackled in the build-up) and Dike, the only thing it can't be is offside. The pass is from the defender. The tackle, you understand, is not a foul, then the defender made and assist to Dike - it can't be offside if the defender has passed the ball.
"If after you understand that Dike was in a position to win the penalty, or if it's not a penalty it's a corner. The three possibilities are a foul to Okay, a penalty or a corner. The only possibility that doesn't exist is the offside, because the defender made the pass. For me, the worst one was the foul Dike received when Asante has the ball inside the box and he was ready to cross, but Dike received a foul.
"One foul out of the box that was not a penalty but Asante couldn't cross because Dike couldn't receive the ball. He took a kick that when you see the image...unfortunately, if we have VAR it's a free kick. Maybe the free kick is saved, maybe they counter attack and score, but it was a free kick."
Corberan was pleased with how his side competed against play-off hunting Millwall but admitted the desire to make things happen in the final third got in the way of some of their play.
"It was a very, very competitive game, I like the spirit and determination of our team to go for the result we wanted," added the Spaniard.
"But sometimes the desire to go for the three points does not allow us to manipulate the ball well enough to move the game more to our side, to moments more beneficial and positive to us.
"That is more positive for them, sometimes this desire moves us to make some fouls which allows them to make a long ball, free-kick, then a corner, after a throw-in, they have this skill, the set-pieces and second ball side.
"Unfortunately we couldn't put the game in an attacking half, we had possibilities, but this is from a tactical perspective. From an emotional perspective every player competed in the level demanded."