It is a general principle that, when raising objections, the burden of proof lies initially with the examiner. This means that objections must be reasoned and substantiated, and must show that, on the balance of probabilities, the objection is well-founded. If this is done, it is then up to the applicant to prove otherwise – the burden of proof shifts to the applicant.
If an applicant provides reasons for questioning the alleged publication date of an internet disclosure, the examiner will have to take these reasons into account.