MARCReader obscure warning: couldn't find 0xa0 in g0=66 g1=69 about pymarc HOT 11 OPEN

import pymarc as pym

with open('C:\\Users\\MY_USER\\Downloads\\IE001_MIL_EL_00017104\\IE001_MIL_EL_00017104.mrc', 'rb') as fh:
    reader = pym.MARCReader(fh, to_unicode=True, force_utf8=True)
    for record in reader:
        for field in record.get_fields('020'):
            if field['a'] is not None:
                print(field['a'])
            elif field['a'] is None:
                print('No ISBN')
            else:
                pass

  11710 couldn't find 0xaf in g0=66 g1=69
   7844 couldn't find 0x80 in g0=66 g1=69
   3205 couldn't find 0xbf in g0=66 g1=69
   1335 couldn't find 0xca in g0=66 g1=69
   1175 couldn't find 0xa0 in g0=66 g1=69
   1042 couldn't find 0xcc in g0=66 g1=69
    299 couldn't find 0xbb in g0=66 g1=69
    122 couldn't find 0xbe in g0=66 g1=69

>>> from pymarc import MARCReader
>>> print(MARCReader(open('BVE0764705.marc21.mrc', 'rb')).next().get_fields('650')[0].subfields[3])
Attività professionale
>>> print(MARCReader(open('BVE0764705.unimarc.mrc', 'rb')).next().get_fields('606')[0].subfields[3])
couldn't find 0xa0 in g0=66 g1=69
Attivit©  professionale

$ for code in iso5426 iso8859-1 marc8; do yaz-marcdump -i marc -o marc -t utf8 -f $code BVE0764705.unimarc.mrc > BVE0764705.unimarc.$code.mrc.new ; done
$ python 
>>> print(MARCReader(open('BVE0764705.unimarc.iso5426.mrc', 'rb')).next().get_fields('606')[0].subfields[3])
couldn't find 0xcc in g0=66 g1=69
Attivit  professionale
>>> print(MARCReader(open('BVE0764705.unimarc.marc8.mrc', 'rb')).next().get_fields('606')[0].subfields[3])
Attivit℗♭ professionale
>>> print(MARCReader(open('BVE0764705.unimarc.iso8859-1.mrc', 'rb')).next().get_fields('606')[0].subfields[3])
couldn't find 0xa0 in g0=66 g1=69
Attivit©℗  professionale

$ yaz-marcdump -o marcxml -t utf8 BVE0764705.unimarc.mrc | grep 606 -A 4
  <datafield tag="606" ind1=" " ind2=" ">
    <subfield code="a">Operatori turistici</subfield>
    <subfield code="x">Attività professionale</subfield>
    <subfield code="2">FN </subfield>
    <subfield code="3">IT\ICCU\MILC\267308</subfield>
$ yaz-marcdump -t utf8 BVE0764705.unimarc.mrc | grep 606
606    $a Operatori turistici $x Attività professionale $2 FN  $3 IT\ICCU\MILC\267308
$ yaz-marcdump BVE0764705.unimarc.mrc | grep 606
606    $a Operatori turistici $x Attività professionale $2 FN  $3 IT\ICCU\MILC\267308

            try:
                if code_point > 0x80 and not mb_flag:
                    (uni, cflag) = marc8_mapping.CODESETS[self.g1][code_point]
                else:
                    (uni, cflag) = marc8_mapping.CODESETS[self.g0][code_point]
            except KeyError:
                try:
                    uni = marc8_mapping.ODD_MAP[code_point]
                    uni_list.append(unichr(uni))
                    # we can short circuit because we know these mappings
                    # won't be involved in combinings.  (i hope?)
                    continue
                except KeyError:
                    pass
                if not self.quiet:
                    sys.stderr.write("couldn't find 0x%x in g0=%s g1=%s\n" %
                        (code_point, self.g0, self.g1))