The original offering was Cameron would do a great renegotiation and then we would have a referendum whether to accept the 'new deal for Britain'. Those with memories that go back to 1973/4/5 will find that vaguely familiar.
In reality he came back with next to nothing, but he couldn't drop the referendum promise. So the referendum went ahead with the renegotiation quietly forgotten about. The Remain side certainly didn't trumpet Cameron's 'successful' renegotiation then because anyone could see it was worth diddly squat.
The official Government booklet sent to all households does mention "The UK has secured a special status in a reformed EU", but the bullet points following are all things that we already had (such as not needing to join the Euro). If anyone knows what this "reformed EU" was I would be grateful for further details, since anything substantive would require TFEU amendment (or so I am told).
"Ever closer union" is a fairly central principle of the whole thing. Negotiating it away was a big deal.