I had seen that article previously and it does seem to cover the situation more comprehensively than most. It is worth remembering that these are all pretty small companies, and/or companies with small percentages of their business as export. As far as Brexit is concerned the UK left the EU a year ago and Dec 30 2020 was the end of the transition period. There were only 2 possible outcomes of Brexit discussions therefore as from January 1st 2021. A trade deal or no trade deal and a reversion to WTO terms.
The change due to take place in terms of trade between the EU and UK has therefore been known for at least a year, the only potential variation being whether WTO tariffs were applied or zero tariffs. You could perhaps forgive smaller companies for not understanding Rules of Origin* but any company exporting other than only within the Single Market would already be aware of that. The other change was the management of VAT...specifically the addition of VAT at point of sale, but not at the customs border, for complete shipments under £135 in value. That is however originally an EU regulation, implemented from January 1st 2021 by the UK, but delayed until June for implementation by the EU. So none of that should have been a change that was not planned for, assuming these companies have accountants or finance directors, for whom all of this is basic to their roles.
* note also that the only rationale for insistence of rules of origin within a trade deal is to ensure trade barriers/tariffs are maintained for goods originating from a country with whom you do not have a reciprocal trade deal. The EU insisted on rules of origin to protect its single market. The UK wants to abolish rules of origin and plans to push for that as it it takes the Chair of the WTO. ROI makes no sense in a global market. The way bikes are assembled is one example...but only a small market. Car manufacture is far bigger and has the same component assembly situation as bikes. Car manufacture was exempted from ROI in the UK//EU trade deal. I wonder why?