The adjectival expression cut and dried means “already made up for use,” or “predetermined.”
Here are some examples of a mistaken use of the expression from the web:
there are no cut and dry rules
A cut and dry case for the courts of law.
Floyd’s NFL decision not so cut and dry
According to the OED, the expression originated in reference to the sale of herbs. Instead of hunting and picking their own fresh herbs in the wild, customers could buy the herbs already “cut and dried” from a herbalist.
Like so many English idioms that require some knowledge of grammar to understand, cut and dried seems to have joined first come, first served in the limbo of incorrectly heard expressions. The errors occur because of an incomplete understanding of verb tenses.
With cut and dried, the past form of the irregular verb “cut” is apparently regarded as being in present tense. The speaker chooses “dry” in the mistaken idea that “cut” is present tense.
With first come, first served, the second verb loses its past tense ending because the speaker wants it to agree with “come,” which is seen as a present tense verb.
I have seen attempts to justify the acceptability of “cut and dry” and “first come, first serve” by claiming that cut and dried and first come, first served are “hyper-correct, less common” versions. Nonsense. They are the original expressions.
Here’s a link to an article that I wrote on the topic of “first come, first served.”