The question of the formal requirements for the transfer of the right to claim priority is still very much an open one at the EPO. Several EPO Board of Appeal (BoA) decisions have taken different approaches to it, not least because the corresponding formal requirements are not spelled out explicitly, neither in the European Patent Convention (EPC) nor in the implementing regulations.

But a new BoA decision now provides some guidance on this topic.

In this case, the priority application was a US provisional filed by the inventor. The right to claim priority from that application had been validly transferred from the inventor to a Taiwanese company. However, the European application claiming priority from the US provisional had been filed by a Mauritius company, so the question was whether the right to claim priority had been properly transferred from the Taiwanese company to the Mauritius company.

In its decision, the BoA first stated that, based on the wording of the relevant EPC provisions on priority, the transfer of the right to claim priority must have taken place before the filing of the European application claiming priority. (The same holds where the European application was originally filed as a PCT application designating EP – i.e. in that case, the right to claim priority must have occurred before the filing date of the PCT application).

Furthermore, the BoA stated that since the right to claim priority is a property right, it is a distinct right from that of ownership of the priority application itself. As a result, the transfer must relate (also) to the right to claim priority, whereas the mere transfer of ownership of the priority application is not sufficient.

The BoA also held that, in any case, the burden of proving a valid transfer of the right of priority lies with the patent owner, since it is the party claiming that right, and all the more so since the patent owner alone has access to the relevant evidence. In terms of the standard of proof, the BoA held that the standard is “beyond reasonable doubt”, rather than being based on the “balance of probabilities”.

For its further assessment, the BoA then took into consideration the following laws:
1. The law of the country where the priority application was filed (“lex originis” );
2. The law of the country where the later application was filed (“lex loci protectionis” );
3. The law of the country agreed upon in the related contract (“lex loci contractus“);
4. The law of the country where at least one of the parties to the transfer has its residence (“lex domicilii“).

The BoA did not state which of the above laws 1 to 4 is the appropriate law – it did not have to do so, because in the case before it the patentee’s case failed when considering each one of those laws. Nevertheless, in considering the patentee’s case the BoA gave some additional guidance that may be helpful in future cases.

Specifically, with respect to the “lex originis”, the BoA concluded that the right to claim priority could not be held to have been transferred before the filing date of the European application by way of a retroactive agreement signed after that filing date, irrespective of whether such agreement would be validly retroactive in the “lex originis” country (here, the US).

Even though this new BoA decision is not binding on future BoA cases, it represents an important precedent and contains guidance on certain formal requirements that must be met for the transfer of the right to claim priority to be acknowledged as valid by the EPO. This new BoA decision therefore represents an important milestone both for European patent applicants and for third parties in assessing the validity of a priority claim at the EPO.

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