What’s interesting is that the Form 990 instructions don’t address this, but they reveal that PTIN’s are not confidential.

“Enter the paid preparer's PTIN, not his or her social security number (SSN), in the “PTIN” box in the paid preparer's block. The IRS won't redact the paid preparer's SSN if such SSN is entered on the paid preparer's block. Because Form 990 is a publicly disclosable document, any information entered in this block will be publicly disclosed”