Since converting all the preset scenarios to the boes format, it has become impossible to load save files from before this time, because there is an exception for preset scenarios that bypasses the normal resolution process.
In general it should be possible to have exs and boes scenarios that otherwise have the same name, without conflict; but in the case of the preset scenarios, I would expect it to redirect to the boes if the exs is not present.
(However, note that dropping in the exs version of the preset scenarios should also be supported.)
Since converting all the preset scenarios to the boes format, it has become impossible to load save files from before this time, because there is an exception for preset scenarios that bypasses the normal resolution process.
In general it should be possible to have exs and boes scenarios that otherwise have the same name, without conflict; but in the case of the preset scenarios, I would expect it to redirect to the boes if the exs is not present.
(However, note that dropping in the exs version of the preset scenarios should also be supported.)