Sometimes you can't quantify actual avoided things. For example you can't prove that a regulation stove actually prevented what could have been a kitchen fire.

Self-promotion is incredibly difficult for some people.

fair, but it's better to point out the solution:

"learn how to be better at self promotion"

Do you have another solution to this issue?

Find someone to champion your work. Also, if you aren't already, start praising others' work in the hopes that they will reciprocate.

The caveat to this is to make sure hope doesn't turn into expectation. Expectation can turn into sourness when the others don't reciprocate. Also, some people feel when you do something just because you expect something in exchange, and that tends to make them not reciprocate.

And the people it comes easy to tend to be labeled as narcissistic, resulting in animosity. It's a double-edge sword.

Better yet, be in a work culture where people happily give credit to and praise others.