I have heard that "During/Over/In" can be used interchangeably. However, both "During and Over" can be used with both the present perfect continuous and the past perfect continuous, but "In" is only works with the present perfect continuous. I am going to make up two examples below.
(1) During/Over/In the last three weeks, I have been looking for a cheap sports car. Finally, I have found a great deal.
(2) During/Over the last three weeks, I had been looking for a cheap sports car. Yesterday, I found a great deal.
Some people told me that "during, over, and in" refer to a period from a time three weeks ago until a recent time. That means you started looking for a cheap sports car three weeks ago and continued looking for one until recently. However, "in" extends the time period up to now. So, it cannot be used to relate to an event that may or may not end right at this moment.
My question is: Is it grammatically wrong to use "In" in my second sentence?