A flurry of closed-door meetings and public displays of support over the last few days signal that the vote is much more than a change to the country’s founding document – it’s a ballot on Xi’s absolute authority.

And it’s for just that reason, analysts say, that it will be worth watching to see just what the final number in favour will be.

Much of the lobbying for the amendments, which include plans to scrap the two-term limit on the presidency, has taken place in camera but there have been several choreographed reminders for the public of the endgame.

On Wednesday, Xi joined the Guangdong delegation for a panel discussion, telling the delegates that “he totally agreed with the constitutional revision”.

According to a deliberately worded text released by state media, the president said the party had solicited input from various sectors and the revision “reflected the common will of the party and the people”.

It was the first time that he had commented publicly on the amendments, and it sent a clear message from China’s most powerful leader in a decade.

The six other members of the Politburo Standing Committee – the country’s de facto most powerful body – drove the message home the same day, dutifully pledging their full support to the changes at other provincial panel sessions.

The amendments were the will of the people and would strengthen the guiding political principle of the party’s overall leadership, they chimed.

Two days earlier, NPC secretary general Wang Chen sought to give the changes a veneer of wider approval, telling the 3,000 delegates that the decision to scrap the term limit was in response to the overwhelming demand from the grass roots.

“During consultations and surveys at the grass-roots level, many regions, departments and members of the party and the public have unanimously called for the rules on presidential term limits in the constitution to be revised,” Wang said.

The unified rallying call from the top left no doubt as to how they wanted the delegates to vote in what has been described as the most controversial changes to the constitution in two decades.

And that is why a lower-than-expected yes vote could undermine the legitimacy of the revision and challenge Xi’s authority. Even though the bill is set to be approved, the leadership needs to secure enough backing to at least give the appearance that it is not a top-down decision.

Beijing-based political analyst Wu Qiang said he thought the changes would pass with a “very high approval rate” because it was exactly what the carefully selected lawmakers had been chosen to do.

“Xi has hand-picked almost all of the delegates on the basis of their reliability and loyalty,” Wu said.

Wuhan University law professor Qin Qianhong agreed but said there might be still some absentee or even opposition votes.

“Nobody wants to appear intolerant of dissenting opinion just to secure 100 per cent approval,” Qin said.

But there is a very clear limit to that “tolerance”. A source from the legal community said many Chinese constitutional scholars were told not to voice their views on the amendments – at least until it was all over.

“An official of a provincial-level law society told me that they had been asked by the China Law Society to ban all of its members from organising or taking part in any academic conference on constitutional amendments until the closing of the Two Sessions,” the source said.

So sensitive is the issue that most of the top lawmakers and political advisers gathering in Beijing in the last week or so have simply walked away when asked about the changes.

Analysts said the leadership was aiming for a higher level of endorsement for the proposal on the NPC floor than the two previous constitution amendments in 1999 and 2004.

In 1999, just 21 of the 2,860 or so delegates voted against and 24 abstained from the amendment to include late paramount leader Deng Xiaoping’s “theory” in the national constitution.

Five years later, the opposition was even more muted – 10 of the 2,890 delegates voted against and 17 abstained from a constitutional revision to include former president Jiang Zemin’s signature “theory of the three represents” and protection for private assets in the document.

On Sunday, anything but a landslide could tarnish on the newly revised constitution.

Rana Mitter, professor of modern Chinese politics at the University of Oxford, said he would be immensely surprised to see any opposition votes to the draft constitutional changes, adding: “It would be clearly outside the bounds of possibility to have significant opposition to this.

“I think there will be a very strong push to have as few of those [opposition] votes as possible … Consensus, or the appearance of consensus, will be ... a process of bargaining behind the scenes.”

And every vote counts – just ask Ling Jihua, the former top aide to Xi’s predecessor, Hu Jintao.

More than five years ago, Ling was assured of a seat on the party’s Central Committee, making a shortlist for an “election” in which the number of candidates matched the number of vacancies.

But according to a former delegate to the 2012 national congress, there was still some room to manoeuvre.

“The delegates are entitled to vote down some of the candidates in the election, especially when the result will be announced immediately following the election,” the cadre said.

“I remember there was an uproar among the delegates when it was announced that Ling Jihua had the least number of votes at the time. It’s a scenario that seems awkward and humiliating for those unpopular leaders.”

Today Ling is behind bars, imprisoned for life two years ago for corruption, illegal possession of state secrets and abuse of power.

Additional reporting by Nectar Gan and Sarah Zheng