But there was far less overtaking pre-DRS than there is now according to this site [1] which tracks such things. These stats don't include:

The overtaking figures for each race (across all data sets) do not include:

* Position changes on the first lap of the race

* Position changes due to drivers lapping backmarkers

* Positions gained in the pits

* Positions gained due to drivers yielding

* Positions gained when a car has a serious technical

problem; e.g. puncture, accident damage, etc.

[1] http://cliptheapex.com/overtaking/