I suspect the rare ones are typos.
I compiled a list of the distribution of tag-value pairs and there seems to be a lot of typos:
POS: NOUN
tag: Gender, value distribution: {'Fem': 6011, 'Masc': 6167, 'Mas': 1, 'Plur': 1, 'Sing': 1, 'Neu': 1, 'Nom': 1}
tag: Number, value distribution: {'Sing': 8184, 'Plur': 4040, 'plur': 1, 'SIng': 3}
tag: Definite, value distribution: {'Def': 8492, 'Ind': 3752, 'Nom': 1, 'Acc': 1}
tag: Case, value distribution: {'Acc': 5183, 'Nom': 4631, 'Abl': 627, 'Dat': 637, 'Gen': 2302, 'Det': 1, 'ACC': 3}
tag: VerbForm, value distribution: {'Part': 1}
tag: Foreign, value distribution: {'Yes': 24}
tag: Foreing, value distribution: {'Yes': 4}
tag: Degre, value distribution: {'Pos': 1}
tag: Numer, value distribution: {'Plur': 1}
tag: PronType, value distribution: {'Dem': 1}
POS: DET
tag: Gender, value distribution: {'Masc': 6, 'Fem': 7}
tag: Number, value distribution: {'Sing': 8, 'Plur': 4}
tag: Case, value distribution: {'Abl': 5, 'Acc': 6, 'Nom': 4, 'Dat': 1, 'Gen': 5}
tag: PronType, value distribution: {'Art': 11, 'Prs': 1}
tag: Person, value distribution: {'3': 1}
tag: NumType, value distribution: {'Card': 1}
POS: ADJ
tag: Degre, value distribution: {'Pos': 2797, 'Cmp': 33, 'Sup': 76, 'SUP': 1}
tag: Degree, value distribution: {'Pos': 125, 'Po': 1}
tag: Gender, value distribution: {'Masc': 4}
tag: Number, value distribution: {'Plur': 2, 'Sing': 2}
tag: Case, value distribution: {'Acc': 4}
tag: Definite, value distribution: {'Ind': 4}
tag: Foreign, value distribution: {'Yes': 1}
POS: PRON
tag: PronType, value distribution: {'Prs': 125, 'Dem': 56, 'Int': 24, 'Ind': 102, 'Rel': 25, 'PRS': 1, 'Prd': 1}
tag: Person, value distribution: {'3': 41, '2': 13, '1': 21}
tag: Case, value distribution: {'Acc': 81, 'Nom': 66, 'Abl': 37, 'Dat': 36, 'Det': 1, 'Gen': 16}
tag: Number, value distribution: {'Sing': 98, 'Plur': 72}
tag: Gender, value distribution: {'Fem': 82, 'Masc': 72}
tag: Poss, value distribution: {'Yes': 45}
tag: Reflex, value distribution: {'Yes': 9}
tag: Relfex, value distribution: {'Yes': 15}
tag: Definite, value distribution: {'Def': 2, 'Ind': 1}
tag: PronTYpe, value distribution: {'Ind': 1}
tag: Prontype, value distribution: {'Rel': 2}
tag: CCase, value distribution: {'Acc': 1}
POS: VERB
tag: Mood, value distribution: {'Ind': 6072, 'Imp': 468, 'Cnd': 179, 'Sub': 1886, 'Opt': 1216, 'Adm': 2429, 'Int': 1, 'Def': 1, 'Indi*': 1, 'Nom': 1, 'Des': 3, 'Ipm': 1}
tag: Tense, value distribution: {'Fut': 112, 'Pres': 5317, 'Imp': 2719, 'Past': 2871, 'Pqp': 2, 'Prs': 1, 'Impt': 1}
tag: Person, value distribution: {'2': 2999, '1': 2808, '3': 5266}
tag: Number, value distribution: {'Sing': 5840, 'Plur': 5037, 'Sign': 2}
tag: Polarity, value distribution: {'Neg': 2}
tag: VerbForm, value distribution: {'Part': 615, 'PART': 1, 'Inf': 1, 'Past': 1}
tag: MMood, value distribution: {'Ind': 1}
tag: Case, value distribution: {'Nom': 1, 'Acc': 1}
tag: Definite, value distribution: {'Def': 2}
tag: Gender, value distribution: {'Fem': 1, 'Masc': 1}
tag: MVerbForm, value distribution: {'Part': 1}
POS: ADV
tag: AdvType, value distribution: {'Loc': 73, 'Man': 302, 'Deg': 79, 'Tim': 114, 'Cau': 13}
tag: Abbr, value distribution: {'Yes': 3}
tag: Degree, value distribution: {'Pos': 1}
POS: ADP
tag: Case, value distribution: {'Acc': 20, 'Abl': 26, 'Nom': 10, 'Dat': 1, 'Gen': 1}
tag: AdvType, value distribution: {'Loc': 4}
tag: Gender, value distribution: {'Masc': 1}
tag: Number, value distribution: {'Sing': 2}
tag: Definite, value distribution: {'Ind': 1}
tag: PronType, value distribution: {'Prs': 2}
tag: Person, value distribution: {'1': 1}
POS: AUX
tag: Tense, value distribution: {'Pres': 50, 'Imp': 28, 'Past': 12}
tag: Person, value distribution: {'2': 25, '3': 37, '1': 26}
tag: Number, value distribution: {'Sing': 48, 'Plur': 39}
tag: Mood, value distribution: {'Ind': 42, 'Adm': 25, 'Sub': 12, 'Opt': 12}
tag: VerbForm, value distribution: {'Part': 2}
tag: N0umber, value distribution: {'Sing': 1}
POS: PROPN
tag: Definite, value distribution: {'Def': 2410, 'Ind': 579, 'Acc': 1, 'DEF': 1}
tag: Gender, value distribution: {'Masc': 1810, 'Fem': 1141, 'Mac': 3}
tag: Number, value distribution: {'Sing': 2714, 'Plur': 217, 'Sin': 1}
tag: Case, value distribution: {'Nom': 1347, 'Dat': 91, 'Acc': 776, 'Gen': 810, 'Abl': 55, 'Det': 1, 'GenDat': 1, 'Geb': 1}
tag: Degree, value distribution: {'Pos': 10}
tag: Foreign, value distribution: {'Yes': 178}
tag: Degre, value distribution: {'Pos': 66}
tag: Foreugn, value distribution: {'Yes': 3}
tag: NumType, value distribution: {'Card': 2, 'Ord': 1}
tag: Foreing, value distribution: {'Yes': 6}
tag: Defenite, value distribution: {'Def': 1}
tag: Deegre, value distribution: {'Pos': 1}
tag: Foreig, value distribution: {'Yes': 2}
POS: NUM
tag: NumType, value distribution: {'Ord': 53, 'Card': 596}
tag: Gender, value distribution: {'Fem': 15, 'Masc': 9}
POS: PART
tag: PronType, value distribution: {'Prs': 1}
tag: Person, value distribution: {'3': 1}
tag: Number, value distribution: {'Sing': 2}
tag: Gender, value distribution: {'Fem': 2}
tag: Case, value distribution: {'Acc': 1, 'Nom': 1}
tag: Definite, value distribution: {'Ind': 1}
POS: ACC
tag: Case, value distribution: {'Acc': 1}
tag: Gender, value distribution: {'Masc': 1}
tag: Number, value distribution: {'Sing': 1}
tag: Definite, value distribution: {'Ind': 1}
POS: AADV
tag: AdvType, value distribution: {'Tim': 1}
POS: NUON
tag: Gender, value distribution: {'Fem': 1}
tag: Case, value distribution: {'Nom': 1}
tag: Definite, value distribution: {'Def': 1}
tag: Number, value distribution: {'Sing': 1}
POS: NOM
tag: Definite, value distribution: {'Ind': 1}
tag: Number, value distribution: {'Plur': 1}
tag: Gender, value distribution: {'Masc': 1}
tag: Case, value distribution: {'Acc': 1}
POS: PROPM
tag: Gender, value distribution: {'Masc': 1}
tag: Definite, value distribution: {'Def': 1}
tag: Number, value distribution: {'Sing': 1}
tag: Case, value distribution: {'Nom': 1}