Trouble distinguishing meanings in verb past tense

Imagine a map titled "Settlement 1904-1914". In the key, red is labeled as "area that was settled during the time period".

From context, this seems like it means areas newly settled in the time period, not all areas that had the state of "being settled" during the time period (i.e. those which were settled previously and remained settled). I do think it is ambiguous.

Is this actually ambiguous without contextual clues? Or is there a verb tense I’m missing?