I think that's not really adding much when talking about Waqar
I took 1994 as cut off date when it was adopted.
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One neutral umpire per Test was appointed on an experimental basis in 1992, and the system was adopted two years later.
They made their first appearance when a Pakistan captain invited two Indian umpires to stand in a Test against West Indies
www.espncricinfo.com
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No other team has drastic change ONLY in home result like Pakistan . Pakistan did not have change in away record at all. Teams do decline and it will have impact on home and away both.
Pakistan had many good players in that period with Wasim, Waqar, Saqlain, Inzzy, Akhtar, Moyo, Anwar, YK, Mushtaq and yet saw home record tumbling big time. If team had declined big time and had the same trend away then it's understandable, but that's not the case with Pakistan. You can even make a case for Pakistan having best players playing for them collectively when this happened.