I bet many of those have clauses that say that if UK diverges from EU and so cannot have seamless trade with EU at the same time those trade continuation agreements also become null and void.
I can see such being included in agreements signed AFTER the 2016 vote, for agreements before I would be surprised if such exist, after all, even the EU never thought anyone would want to leave the bloc. IF the EU never thought of it why would third countries be concerned about a member leaving to include it in their agreements?
I am not saying it is not possible, but I would be surprised post 2016.
Those continuation agreements are only about February 1st to December 31st of 2020 (unless possibly the transition period may get extended after all) because only during the transition period the UK will actually remain compliant with EU rules and regulations, but will already no longer be an EU member.
During the transition phase the EU will still treat the UK as a (now only non-voting!
) member state, but after Brexit formally taking effect on February 1st all treaties with external third countries
will formally lose effect, so the UK will be dependent on those third countries
agreeing to continue as if the UK was still an EU member even though it actually won't be (just an EU-compliant non-member).
That is what those continuation agreements are about, and as mentioned above they only apply to the transition phase but not beyond that.
And new agreements of the UK with those other countries will almost certainly be dependent on the new relationship the UK will have with the EU and those will be limited by the most favoured nation
clauses those other countries already have with the EU, so it will be very difficult if not impossible to get any better deals alone.