You will know you have really made it when it doesn't even occur to either of you to compare the performance of the other to a past partner, the same way that how good you are at cooking or account-keeping doesn't matter to the person who loves you.
Exactly. If you're still "keeping score" on skills or numbers (some jealousy may always be there if you know about their past), I'd reconsider any serious decisions, such as engagement or marriage, at the time. There comes a point where it really shouldn't matter at all.
And as someone who had made their partner tell me everything about their past -- DON'T DO IT. He respects not knowing every detail of mine and I wish I had done the same for him. The stories have haunted my mind for years. It's damage that is not easily undone. We waited with each other for 3 years, and I don't want to say that it really canceled out the past...but in many ways, it did for the two of us. I don't regret it for a second. Worth the wait.