The DUP should be wary. In politics, the appearance of denial - even denial carefully framed in words which are, strictly speaking, correct - can be a dangerous trap to fall into. In this case, it may have given Sinn Fein an important bargaining chip.
There were no denials from Sinn Fein when the Belfast Telegraph published leaked US diplomatic cables showing that the US and Irish governments, as well as Sinn Fein, all believed there had been secret contacts between Sinn Fein and the DUP in 2004. Sinn Fein was careful not to deny this.
Sinn Fein keeps a careful record of such contacts, as Sir Patrick Mayhew - the former secretary of state - found out to his cost.
Sir Patrick, a barrister like some DUP advisers, crafted his early response to questions about contact with Sinn Fein in terms which were technically correct, but didn't reveal the whole picture and which people took for denial.
When Sinn Fein produced a full record of everything that passed through the back channel from Gerry Adams to the Cabinet table, Sir Patrick was embarrassed, but he insisted he had told the truth. It hadn't amounted to negotiations taking place, he said.
The problem is that people tend not to remember the exact, carefully parsed words of a statement; they form a general impression and, if their general impression doesn't meet the facts, they tend to feel misled.
Sinn Fein has already discussed a back channel with DUP members on a number of occasions. They told Jonathan Powell, Tony Blair's chief of staff, about it and it comes up frequently in the WikiLeaks cables.
In 2004, they discussed it with Alan McFarland, a member of the UUP negotiating team, and another witness in the Leeds Castle talks.
Both men have now retired from politics and have no axe to grind. It happened after DUP members took pictures of Lady Hermon - then a UUP MP - having lunch with Pat Doherty of Sinn Fein.
Mr McFarland recalls: "Later, a senior member of Sinn Fein told us the DUP were in no position to embarrass Sylvia because they were in direct, but deniable, contact with Sinn Fein themselves."
The Sinn Fein politician said that Jeffrey Donaldson - a former UUP MP who had joined the DUP in January 2004 - was involved.
Mr Donaldson would have made an ideal interlocutor.
Prior to leaving the UUP, he had negotiated with Sinn Fein and, at the time, he said that he would continue to "exchange pleasantries" with the party after joining the DUP. He now says: "I have nothing to add to the party statement. The only negotiations I am aware of are the ones which took place through the British Government."
He firmly denied that any words he exchanged with republicans made him a go-between for the DUP.
At present, Sinn Fein has nothing to gain from casting any new light on the DUP's statements.
But they know exactly what their understanding was and that could give them a little leverage with the DUP, if they ever need it.
It might be in the DUP's interests to clear up any possible misunderstanding at this stage. Voters appreciate transparency.