Prior use rights: keeping the right to use what you built
By BlockchainSignLast updated
You built something, kept it in-house, and never filed. Years later a competitor patents it and asks you to stop, or to pay. In much of the world there is a defence for exactly this situation — but it turns entirely on whether you can prove what you had, and when. That is where most companies discover their records are worth nothing.
The problem this solves
A patent gives its holder the right to stop others using the invention. Taken literally, that would mean a company quietly using its own process for a decade could be shut down by someone who filed later.
Most patent systems decided that was unacceptable. The answer is a prior use right: a personal defence for someone who already had the invention before the filing date.
It is worth being precise about what it is and is not:
- It is a defence to infringement, not a right to stop anyone else.
- It is personal, and generally transferable only with the business it belongs to.
- It does not invalidate the patent. The patent stands; you are simply not liable to it.
- It usually does not let you expand freely beyond what you were already doing.
It is not the same right everywhere
This is where general advice goes wrong. The threshold differs by jurisdiction, and in one important case it is much higher than people assume.
| Jurisdiction | Basis | What you must show |
|---|---|---|
| France | Art. L613-7 CPI | Possession of the invention, in good faith, on French territory, at the filing or priority date |
| Germany | § 12 PatG | Use, or effective preparations to use, before the filing or priority date |
| United Kingdom | s.64 Patents Act 1977 | A good-faith act, or effective and serious preparations, before the priority date |
| United States | 35 U.S.C. § 273 | Commercial use in the US, beginning at least one year before the earlier of the filing date or public disclosure |
Two differences matter commercially. France protects mere possession — you do not have to have been selling anything. The United States protects only commercial use, and demands a full year of it before the clock stops. A US company that developed something quietly and never commercialised it has no § 273 defence at all.
And it is not universal. Several jurisdictions have no prior use right, so a defence that works in Munich may be worth nothing elsewhere.
The part that costs people the case
The burden of proof sits on you, and the standard is higher than most people expect. French case law asks for evidence carrying a character of sincerity and sufficient certainty.
Then comes the sentence that decides most of these disputes:
Purely internal plans are generally insufficient, because no one can provide proof to themselves.
Your own project folder, your own file timestamps, your own dated PDFs — all of it was produced by the party who benefits from it, and all of it could have been produced last week. A filesystem date is a claim, not evidence.
This is not a technicality. It is the entire reason a whole category of dated-proof services exists.
What is normally accepted
The methods that hold up share one property: the date does not depend on your word.
- A Soleau envelope or e-Soleau deposit with the INPI in France.
- A bailiff's or notary's report recording what was shown to them and when.
- A sealed letter deposited with a notary or a learned society.
- Laboratory notebooks countersigned by someone outside the business.
- A cryptographic timestamp anchored somewhere you do not control.
Where a blockchain timestamp fits
A timestamp is one member of that list, with a specific shape:
What it does. It fixes, beyond your ability to alter it, that a particular file existed in a particular form no later than a particular block. The record sits on a public ledger you do not operate, so it is not proof you provided to yourself. Anyone can check it, years later, without your cooperation and without ours.
What it does not do. It does not prove you invented the thing, that you used it commercially, or that you acted in good faith — all of which the defence may also require. It evidences one element: the date. See proof of existence vs proof of authorship for why that limit matters and where it is still decisive.
Why the privacy matters here specifically. A prior use defence usually concerns something you deliberately kept secret. Depositing the file with an archive means a third party now holds a copy of your unpatented process. Hashing it in your browser and publishing only the fingerprint records the date while the contents stay with you — which is also what keeps the trade secret argument available to you at the same time.
What to timestamp, in practice
The defence is about a state of affairs on a date, so a single file rarely tells the whole story. Records worth fixing:
| Moment | What to record |
|---|---|
| Concept settled | The specification, drawings or design files as they then stood |
| Each significant revision | The set, not just the changed file — a sequence shows development |
| First internal deployment | Build artefacts, configuration, deployment notes |
| First commercial use | Invoices, delivery notes, customer correspondence (essential for US § 273) |
| Before any disclosure | The exact package leaving the building |
A sequence of dated versions is considerably stronger than one dated file: it evidences a development history rather than mere possession on a single day.
The honest summary
Prior use rights are a real and valuable defence, and they are also narrow, personal and jurisdiction-specific. A timestamp does not hand you the defence — it preserves the one element you are otherwise least able to prove, at a cost that is trivial next to the licence you would be negotiating instead.
The records that carry weight are the ones created before anyone was in dispute. That is the only part of this you have to get right in advance.
This page is general information about how these doctrines work, not legal advice on your situation. Prior use is fact-specific and worth taking to a patent attorney before you rely on it.