けんど is 関西方言 according to daijr. I'll make a separate entry for it.

@@ -10,3 +9,0 @@
-</r_ele>
-<r_ele>
-<reb>けんど</reb>

けど	264538469
けれど	25837638
けれども	12292892
けども	3084936
けんど	52699

So move out けれど and けれども, and leave the others? I'll set that up and see if it works.

@@ -7,8 +6,0 @@
-</r_ele>
-<r_ele>
-<reb>けれど</reb>
-<re_pri>ichi1</re_pri>
-</r_ele>
-<r_ele>
-<reb>けれども</reb>
-<re_pri>ichi1</re_pri>

daijs
[補説]「けれども」は中世末、形容詞活用の已然形語尾に接続助詞「ども」が付いてできたもの。近世前期になると、くだけた感じを伴う「けれど」「けど」が生じ、後期には、「けども」が成立した。

https://hinative.com/ja/questions/168002
丁寧さの違いです。
↑ていねい
「けれども」
「けれど」
「けども」
「けど」
↓ていねいではない
敬語を使う相手には、上の二つを使います。
https://hinative.com/ja/questions/1968834
けれどもはけどより丁寧です

different levels of politeness. different registers. 　けれども and けれど should probably be [pol] or [form] tagged.
it's not like けど can just be replaced with any of the others in any sentence (or vice versa). It's like having だ and です in the same entry (which we previously did in んだ and んです but we ended up splitting it). I just think it's confusing.

I was waiting for a case to be made. Both GG5 and ルミナス simply point けど to their けれど(も) entries. I don't think a split is needed.
GG5 has a second sense with the explanaion "〔単に接続的に, あるいは特別の意味なしに〕".  A little hard to gloss.

I suggest splitting out けれど,けども けれども