"I told you so" has no value to a conversation, relationship or business results. 100%
I think it can be very productive to say something like "hey, I'm a little upset because I tried to get ahead of this problem and to me, it didn't feel like my concerns and ideas were taken into account and now we're considerably behind. I'd like to be helpful on these types of problems in the future, can we make a change to support that?"
If the statement is just about ego, it shouldn't be said. If there's something deeper that is causing relationship or business issues, find a way to dig it up and say it clearly with the goal clearly outlined.
"I told you so", perhaps wrapped in a corpspeak package if the recipient is resonant to those frequencies, adds a lot of value in terms of me not having to handle the fallout. Yes, I know some people want to do an awesome job, be noticed or whatever, but the easier solution (and fairer) is to let the fire burn under whoever caused it. OTOH if you find yourself in a situation when you have to clean up mess that was caused by indifference to your own concerns then it simply means you've lost politically, sadly.
So instead of saying, "I told you so" in four words, you stretched it out to 30+ words.
I can almost guarantee that if someone is saying, "I told you so", they've probably also tried to explain to someone why X is a bad idea or why Y isn't going to work the way they think it will, or at all.
Personally I would prefer "I told you so" from anyone I care about instead of these lamentations. Chances are high that I would completely ignore such input depending on the situation if I were the receiver. If I did indeed do a mistake, which doesn't have to be the case in business, it will be easier to learn from it if people communicate directly.
If I am your supervisor chances are that I would package it more friendly, but it depends. More importantly is that we put this conflict behind us. Depending on the relationship it could be "I told you so, next time let us do X".
I think it can be very productive to say something like "hey, I'm a little upset because I tried to get ahead of this problem and to me, it didn't feel like my concerns and ideas were taken into account and now we're considerably behind. I'd like to be helpful on these types of problems in the future, can we make a change to support that?"
If the statement is just about ego, it shouldn't be said. If there's something deeper that is causing relationship or business issues, find a way to dig it up and say it clearly with the goal clearly outlined.