The SMTA appears to set no time limit on the liability for mandatory payments. Is that true?
No. It is true that the SMTA does not explicitly specify a time limit. However, it does so indirectly, by linking liability under the default scheme of payment to availability of your product to others for further research and breeding. Liability to mandatory payments starts when the restrictions on availability start, and stops when those restrictions finish. If the restriction on availability results from your protection of your intellectual property on a variety, liability for payment will typically end after 20 years.
