A few more points...
Firstly the foreskin doesn't always retract behind the head of the penis on all erect uncut dicks. Mine doesn't, for example, and haven't had enough experience to comment on how common it is!

But also doing a google search there ARE dildos with foreskin, or at least an attempt at foreskin... but i think generally they're pretty pathetic. It can't be easy to do...

Consider, the Foreskin Dildo. Call that realisitic? I don't!
Or the Latex Foreskin Prosthetic - a ugly strap on that looks like it could scratch.
And then there's the Replicock. It doesn't even look like that foreskin moves, but it's hard to tell.

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You know, Blackadder, for me socks are like sex. Tons of it about and I never seem to get any.

My Photos:
https://imgur.com/a/80hiRdm