You assume incorrectly.
I'm not sure what table you look at, but https://en.wiktionary.org/wiki/bod#Conjugation , for example, has "does dim" listed in the present tense in the "colloquial forms" table (you may have to click on the "conjugation" bar to open it up) and "doedd e/o/hi ddim" for the past.
Ah, I had not noticed the colloquial forms table. The question, of course, is whether they are colloquial for this region or that region, for this village or that village. Clearly, this Duolingo team is using a particular standard, and it would just be nice if they would install some sort of Tips and Notes to indicate what that standard might be.