遡る: three generations and five years of records
Read tracing a family tree back three generations and checking accounting records back five years, keeping the object and unit of each pastward scope.
Direction toward the past and its unit
遡る (さかのぼる) means to go back or trace back. These examples concern looking into earlier family-tree and accounting records.
Attach 三代前まで and 五年前まで to their respective objects. Three generations is a generational scope; five years is a year-based scope. Neither is a count of people, and the two are not interchangeable durations.
A family-tree investigation and a records check
「家系図を三代前まで遡って調べた。」 (I traced my family tree back three generations.) The family tree was traced back three generations. 調べた reports the investigation; the sentence does not describe changing family relationships.
「会計記録を五年前まで遡って確認した。」 (I checked the accounting records going back five years.) The accounting records were checked going back five years. 確認した reports the check, without guaranteeing every record's accuracy or describing a retroactive legal effect.
Keep each number with its own object
三代 and 五年 both specify how far back the examination went, but their units differ. Keeping generations with the family tree and years with accounting records preserves both objects and scopes.
In the two sentences, 遡って leads into 調べた or 確認した. The reported examination of earlier material does not by itself change that material or establish a new effect for it.
What units do 三代 and 五年 express in these 遡る examples?
Show the answer and why
三代 gives three generations in the family-tree investigation. 五年 gives five years in the accounting-record check. They are different units rather than the same duration or a count of people.