Many of these figures are inaccurate.
I was at two of these events (Cardiff and Bydgoszcz). The figure for Cardiff is an approximation (ie 45,000) The figure for Bydgoszcz is completely wrong. Without the temporary seating, the stadium holds 17,000. there was another 3,636 temporary seats added From GP Site
That takes it to well over 20,000. However, as anyone will tell you, the stadium was completely over sold. Folk were standing on my seat and in the isles without a seat, the bars were permanently packed throughout the meeting and there were tons of folk piled up at the back of the stands with no seat. Estimates range from 25,000 to as high as 30,000 in the stadium. My own guestimate would be 27,000, maybe 27,500... but like I said, anyone who was there will testify to there being far more than 20,000.