I recall this discussion during the "covid" years and at the time, I recall thinking Brompton had no case as a Patent hold water if it is a innovation; if any engineer come to the same logical solution, it is not Patentable (curved top tube is functional). Then there is the Copyright or US design patent that work around a shape like a Kartell chair for example; these are not very strong as the copy has to be exact to be enforceable which was not the case and it was clearly argued on different point in court without success.

Any person who is used to deal with patent would/should have seen that... but, Brompton may have know that at the time and still play the game to scare "cloners" and therefore maintain their sale advantage; cost wise, was it more profitable to sell X bikes between 2017 and 2023 and play for legal fees rather than loosing sales?

When I worked for a company based in Indiana, one of the marketing guy would ask to put "patent pending" on anything even if we knew it was not patentable just to get 1years buffer, discourage the competition while setting up/growing the market shares... Once market shares were up, it was very unlikely customer would swap supplier dur to the specificity of the business...