Another attested form in 19th century: "abysi".

Author: dan-zeman

udapi/block/ud/cs/addmwt.py

@@ -8,7 +8,9 @@
     'abych': {'form': 'aby bych', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=1|VerbForm=Fin'},
     'kdybych': {'form': 'když bych', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=1|VerbForm=Fin'},
     'abys': {'form': 'aby bys', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=2|VerbForm=Fin'},
+    'abysi': {'form': 'aby bys', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=2|VerbForm=Fin'},
     'kdybys': {'form': 'když bys', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=2|VerbForm=Fin'},
+    'kdybysi': {'form': 'když bys', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Sing|Person=2|VerbForm=Fin'},
     'aby': {'form': 'aby by', 'feats': '_ Aspect=Imp|Mood=Cnd|VerbForm=Fin'},
     'kdyby': {'form': 'když by', 'feats': '_ Aspect=Imp|Mood=Cnd|VerbForm=Fin'},
     'abychom': {'form': 'aby bychom', 'feats': '_ Aspect=Imp|Mood=Cnd|Number=Plur|Person=1|VerbForm=Fin'},