Old Saves are dead ?

Savegames last played on a version prior to 10.2 are not supported for migration, savegames with that version might require a migration to 11.0 before migrating to 11.1.

That statement is misleading, in the opposite Update 11 is the first version of Eco that does not require an online connection to play in singleplayer, the server had priorly required an online connection in all cases and so did the client. Correct is that dedicated servers now need an account login and that versions prior to Update 11 can no longer be played due to the new authentication system (which is unrelated to the account login which is the best I can think of you might consider DRM), but savegames can still be migrated under the restrictions I mentioned as it is not necessary to load them up on an old version before Update 11.