OK, here we go.
Why – probably as it didn’t fit the schedule.
When – if you don’t see it on the tour dates page on www.deep-purple.com it is probably not happening.
Can’t find the date – same answer as “When”. But it could possibly be a scam date. (Yes, that has happened in the past.)
The official site will ONLY list dates that have been confirmed. Just because you have seen tickets on sale, or dates posted on other sites that are not official, does not mean the gig is confirmed. When you see the dates here, that is when they are official and confirmed.
Then again – nothing is really confirmed until the band is on stage, right? :-)