You should have asked him "can you elaborate?", if he couldn't then you know he was just looking for a way to lessen his burden of blame on to you.

DH86 and I sometimes feel this, usually after a visit with one of our 5 kids, when they, intentionally or not, make us feel guilty.  I finally told him that yes, we made mistakes and I'm sorry we did.  However, I remember those days and every one of them, we got up and did the best we could for them at a huge cost of time, emotion, money and our relationship.

I doubt if any one of them could have coped with a 5- kid stepfamily, 2 deadbeat ex's and a hectic job.  Perhaps if we'd been more knowledgeable , or had more help, or if we'd had different kids,  things might have turned out better but it was what it was and we gave it our best shot.

Rehashing the past is futile, imo.

I've come to the conclusion that I made mistakes too with my now 16 year old sd and I know my husband also made mistakes. Parenting is hard and we do what we think is best, without hindsight it is tough for us to know in the moment what to do.  

The person who says that they have never made a mistake with the kids/ steps is not living in reality. You make the best decision, based on circumstances, you can at the time. Sometimes it's the wrong one. But, you can't dwell on it. What you can do is revise going forward based on what you now know. Hindsight can give you other options you might have chosen, but it is not going to tell you what should have done. Outcomes vary. What you think you should have done may not have yielded your desired outcome.

"We"? Hmph correct me if I am wrong but why do I have a feeling his idea of you "doing better" = more leniency when it comes to his kid's bad behavior because that's what it ALWAYS comes down to with these dads.

But most of these spineless-in-the-face-of-the-BM-and skids men don't even attempt to parent and are content to erroneously lay blame at the feet of SM, who wasn't even at the scene of the crime.

Many are revisionistic and imagine themselves as great, strict parents; being able to spot flaws in OTHER  parents at a moment's notice. 

life is about mistakes. getting through them, accepting them from yourself, and fixing those things for the future. It's cute that he threw that "we" in there so he can avoid facing his straight on but in reality it's dealing with our own crap that makes us deal with everyone else's better. him diluting his own mistakes isn't going to help him change his outlook. but that's a him thing not a you thing. 

My mistake was taking on responsibilities with SD at the start of our relationship. I thought I was "helping" and had good intentions... but it led to SD resenting me and making a bad attitude even worse. Think: "you can't tell me what to do" reactions. It also led to drama with BM because she felt I was trying to take her place and one up her (she's a very insecure person). It ALSO put a strain on DH and I relationship because he wanted the best of both worlds from me... to do his heavy lifting and "love her as my own", but have ZERO say in any decision making. 

It would have saved EVERYONE a lot of stress if I left everything to bios right from the beginning. But hindsight is 20/20. 

Parents who go into "Disneyland mode" - part of that mode is refusing to accept responsibility and if responsibility is accepted it's half-assed as they roll other people under the bus with them. 
 

A good apology is "yeah I messed up and this is how I'm going to do better" 

A half assed apology that's not even a real apology is " I messed up.....BUT ..... You did too!"

Anyway then he says he did make mistakes and that I  had also made mistakes and WE could have done things differently in the very beginning.

"he says he did make mistakes" .... then if he was really ready to accept responsibility he should have left that sentence right there. Him trying to add you to the mix of HIS mistakes was a way to deflect which now he has turned into a blame game.
 

If you accept responsibility for your actions then that's what it is but trying to force other people to accept responsibility for their actions is futile  

And no there is no WE in a kid you didn't create nor single-handedly raise from birth. Those skids came pre-programmed from their bio parents and you had nothing to do with that. If his daughter was disrespectful to you it's because of her bioparents raising her with no hometraining nor respect for her elders ... that "WE made mistakes" is a conversation he needed to have with his ex-wife

 

I want to know what he thinks I should have done differently! And how HE contributed to my actions!

No you do not because he's trying to shift the focus/blame (of why his daughter was disrespectful of you) on to you. I wouldn't even go down that rabbit hole with him where he puts you in a position where you now have to defend yourself. 
 

It's just a ruse to get himself out of the "hot seat" by putting someone else (aka you) there instead. 
 

If he was really concerned about what you could have done differently he would have addressed that before now. 
 

Kind of convenient how he brings that up when it's time for him to take responsibility for himself / his actions. 

isnt that deep after all.

I think these parents that see the results of years of non parenting and guilty parenting, they NEED someone to help them shoulder the pain with them. Like we SHARE in their ineptitude.

The past is only an asset if you learn from it and build to a better future because of those lessons.

Him not even recognizing them or deluding himself about those lessons, meh.

Ask him to elaborate on what HE things HE could have done differently. When he tries to pin it on you, explain to him what you would have done differently..... Specifically, what you would have refused to tolerate and would have applied escalating misery inducing consequences in response to.

Guilt, .... not something I think anyone should invest in.  It is far better to invest in reviewing the learning elements from past experiences.

IMHO of course.