I know that LEGO bricks have changed over the years, with regards to moulding pip locations, element ID numbers printed inside, etc, but I was wondering if anyone knows when these changes happened?
What year was the pip moved from on the side of the brick to on the stud?
What year did they start printing the element ID on the elements?
What year were the heads changed from solid stud to recessed stud?
The reason I ask is because I have started to collect earlier sets from the 1980s and 1990s and these are used sets. I want to know if they are the original parts or if they have been substituted for newer, cleaner parts.