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.
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".