It looks like gnparser can handle the "bis" suffix just fine. For example, this name gets parsed correctly:
Curvularia ocimi Rashmi Dubey & A.K. Pandey bis
Also, the "ter" suffix is interpreted correctly, if it is somewhere in the middle of the author string. For example, this name gets parsed correctly:
Phaeoisariopsis hibiscina S.K. Majumdar, S. Singh ter & Anuradha
But things break down when the "ter" suffix is at the end of the author string. For example, in these species names (all from the 2021-07-29 version of the Catalogue of Life) the author suffix is interpreted as an epithet by gnparser:
Pseudocercosporella endophytica Crous & H. Sm. ter
Beltrania pseudorhombica Crous & Y. Zhang ter
Botryosphaeria sinensis Y.P. Zhou & Y. Zhang ter
Chaetopsina beijingensis Crous & Y. Zhang ter
Dematiocladium celtidicola Crous, M.J. Wingf. & Y. Zhang ter
Helicascus unilocularis J. Fourn. & Y. Zhang ter
Lasiodiplodia chinensis Z.P. Dou & Y. Zhang ter
Setophaeosphaeria badalingensis Crous & Y. Zhang ter
Setophaeosphaeria hemerocallidis Crous & Y. Zhang ter
Toxicocladosporium pini Crous & Y. Zhang ter
Ascotricha longipila X.L. Cheng & Wei Li ter
Ascotricha parvispora X.L. Cheng & Wei Li ter
Ascotricha sinuosae (Wei Li ter & X.L. Cheng) X.L. Cheng & Wei Li ter
Phaeoisaria sedimenticola X.L. Cheng & Wei Li ter
IPNI uses the suffixes "bis" or "ter" to distinguish different authors with the same name: https://www.ipni.org/about#about-the-authors-dataset
It looks like gnparser can handle the "bis" suffix just fine. For example, this name gets parsed correctly: Curvularia ocimi Rashmi Dubey & A.K. Pandey bis
Also, the "ter" suffix is interpreted correctly, if it is somewhere in the middle of the author string. For example, this name gets parsed correctly: Phaeoisariopsis hibiscina S.K. Majumdar, S. Singh ter & Anuradha
But things break down when the "ter" suffix is at the end of the author string. For example, in these species names (all from the 2021-07-29 version of the Catalogue of Life) the author suffix is interpreted as an epithet by gnparser:
Pseudocercosporella endophytica Crous & H. Sm. ter Beltrania pseudorhombica Crous & Y. Zhang ter Botryosphaeria sinensis Y.P. Zhou & Y. Zhang ter Chaetopsina beijingensis Crous & Y. Zhang ter Dematiocladium celtidicola Crous, M.J. Wingf. & Y. Zhang ter Helicascus unilocularis J. Fourn. & Y. Zhang ter Lasiodiplodia chinensis Z.P. Dou & Y. Zhang ter Setophaeosphaeria badalingensis Crous & Y. Zhang ter Setophaeosphaeria hemerocallidis Crous & Y. Zhang ter Toxicocladosporium pini Crous & Y. Zhang ter Ascotricha longipila X.L. Cheng & Wei Li ter Ascotricha parvispora X.L. Cheng & Wei Li ter Ascotricha sinuosae (Wei Li ter & X.L. Cheng) X.L. Cheng & Wei Li ter Phaeoisaria sedimenticola X.L. Cheng & Wei Li ter