Graham Andrew bought the 33,600-piece Wildlife puzzle and recruited 200 jigsaw fans to complete it, to raise money for local charities.
He was left with four holes in the giant puzzle and had to ask the Barcelona manufacturer to re-cut them.
The pieces have arrived and the puzzle should be completed on Friday.
Volunteers began piecing together the 5.7m (18.7ft) by 1.57m (5ft) picture of jungle creatures at a hall in Reepham on 14 August.
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It was almost complete two weeks later, but, as reported by ITV, four pieces were missing.
"Four out of 33,000 isn't that bad," Mr Andrew told the BBC.
"I had bought a second puzzle just in case this happened. We sifted through for ages to find the pieces, and I was thrilled when we did."
However, Mr Andrew realised the jigsaws were not identical and the back-up pieces did not fit.
"I considered squishing them in, but decided it had to be done properly so I asked the company to re-cut them," he said.
He had to send the surrounding pieces to the Spanish company so they could accurately make replacements.
It is not yet known how the pieces went missing, but he said they probably fell into a handbag or "got stuck on a granny's cardigan" as she was helped out.
Mr Andrew raised funds for the Norfolk and Norwich Hospital children's wards and Reepham nursery by asking people to sponsor puzzle pieces.
The jigsaw will be displayed at the hospital and also taken to Addenbrooke's Hospital in Cambridge.

Keane, 23, who has played for England at under-19, under-20 and under-21 levels, will report to St George's Park on Tuesday with the rest of the squad.
Gareth Southgate called him up after Johnson was ruled out of Saturday's World Cup qualifier against Malta.
On Monday, Andros Townsend replaced the injured Raheem Sterling in the squad.
Crystal Palace's Townsend, 25, has played 11 times for his country and scored three goals, but was not selected for Euro 2016.
He has played in all seven of Palace's Premier League games since joining from Newcastle for £13m in the summer.
England, led by interim manager Southgate, face Malta on 8 October and Slovenia three days later.
No details have yet been given on Manchester City player Sterling's injury.
Keane has featured in all of Burnley's Premier League games this term.
Between 2013 and 2016, the former Manchester United trainee made 16 appearances for the under-21s side under Southgate.
Goalkeepers: Fraser Forster (Southampton), Joe Hart (Torino, on loan from Manchester City), Tom Heaton (Burnley)
Defenders: Ryan Bertrand (Southampton), Gary Cahill (Chelsea), Phil Jagielka (Everton), Michael Keane (Burnley), Danny Rose (Tottenham), Chris Smalling (Manchester United), John Stones (Manchester City), Kyle Walker (Tottenham)
Midfielders: Eric Dier (Tottenham), Jordan Henderson (Liverpool), Alex Oxlade-Chamberlain (Arsenal), Michail Antonio (West Ham), Jesse Lingard (Manchester United), Theo Walcott (Arsenal), Dele Alli (Tottenham), Andros Townsend (Crystal Palace)
Strikers: Wayne Rooney (Manchester United), Marcus Rashford (Manchester United), Daniel Sturridge (Liverpool), Jamie Vardy (Leicester)

They had previously hoped to have a deal for the Championship club, who are in administration for the third time in four years, agreed by Friday.
The Bulls said in a statement "it had not been possible to complete the due diligence in the time available" but work would continue over the weekend.
Joint administrator Gary Pettit asked fans to "remain patient".
He added: "My legal team and my colleagues will continue to work hard over the weekend to give every prospect of success for the survival and renaissance of Bradford Bulls.
"Obviously, we wish to end the uncertainty for all concerned as quickly as is possible. We recognise and understand the human aspects for everyone (and their families) who has the best interests of Bradford Bulls at heart.
"I would reiterate that it is crucial we obtain the right deal - rather than the quickest deal - for the club's future."
An attempt at what is said to be the largest jigsaw puzzle on the market was nearly scuppered when four pieces went missing "somewhere in Norfolk".
[NEXT_CONCEPT]
Burnley defender Michael Keane has been handed his first international call-up after Stoke's Glen Johnson withdrew from the England squad through injury.
[NEXT_CONCEPT]
The joint administrators of Bradford Bulls have extended the deadline to buy the club to Monday, 19 December.