Because the club will have provided it when it suited them?
Only read the rest of this if you are really interested. It's just a few thoughts.....
If this is about external evidence then I think it will boil down to the panel's interpretation of the rules. Guidance was included in 2020 (coincidentally) that the club had to make best efforts (or some such wording) to obtain third party information when requested. When the investigation started there was no such rule/guidance. So I imagine the club's position will be that they can't apply the 2020 guidance to an investigation started in 2018 and there was therefore no requirement to provide any third party information to the investigation. I imagine the PL's argument is that they can (remember the rumours from early 2024 that the club was challenging the application of new rules to earlier periods?), and that the fact that the club provided external evidence to the panel is proof they didn't make best efforts during the investigation.
The precise-wording finding of the Leicester case may help the club as well.
At the end of the day, the panel may well take the view, as CAS did, that if the club had provided the evidence earlier then there would have been no need for the disciplinary process at all and so the club has made a mockery of the PL's whole investigative process. The panel would naturally side with the PL in that case to discourage other clubs from withholding information in the future. I wouldn't be surprised by that at all.
As I say, just a few thoughts.
And all imh and poorly formed o, of course.