>>> import pymupdf
>>> pymupdf.version
('1.24.4', '1.24.2', '20240516000001')
>>> doc = pymupdf.open("test3.pdf")
>>> doc._get_page_labels()
[(0, '<</S/A>>'), (13, '<</S/r>>'), (15, '<</S/D>>')]
>>> doc[0].get_label()
'B'
First page label supposed to be 'A' ...
Please take a look.