The works came to light after Bonhams contacted the Art Loss Register while carrying out their own due diligence on a box of 34 Appel drawings sent for valuation with a view to consignment.
The storage and logistics company which had sent them to Bonhams told ALR the box was one of eight found inside a warehouse they had purchased years earlier. It had no documentation concerning the boxes, said the ALR, and it was not until a warehouse employee researched 'Karel Appel', whose notes and signatures adorn most of the works, that they realised the boxes were worth more than mere salvage.
It transpired that the works had been lost in transit in December 2002. They comprised a crate of eight boxes containing drawings, sketches, notebooks and mixed media works by the artist, who had sent them to the newly created Karel Appel Foundation in Amsterdam.
The loss was reported at the time to law enforcement and the ALR, who registered the works on their database of stolen, looted, and missing artwork.
After five weeks of what the ALR described as intense negotiation with the logistics company and their solicitors, a settlement was finally reached, with the company agreeing to release their claim to the artwork.
Christopher A. Marinello, a lawyer and chief negotiator for the Art Loss Register said: "This case highlights the responsibility of companies who store and transport works of art.
"With last year's BBC statistics suggesting that over 90% of UK museum collections are kept in storage, the concept of positive registration and due diligence should form part of logistics companies' standard operating procedures.
"Logistics companies store and move millions of pounds worth of art every year but rarely check with the ALR. Highly secure, fine art storage facilities have opened worldwide, from New York to Singapore.
"These storage complexes are the new Swiss bank vaults and no one but the proprietors know what is going in and out of there. While the owners of such facilities are staunchly opposed to having stolen art on their premises, they are reluctant to perform due diligence searching for fear that they will lose business to competitors who may guarantee a more discrete service."
And he warned: "Unless and until fine art storage and shipping companies unite and agree to police themselves, it may be necessary to push for legislation requiring the industry to become more transparent."