- Adjectives modify nouns
- Adverbs modify verbs, adjectives, and other adverbs.
Sometimes in SC we must choose which to use according to the meaning.
"¢ supposed Mediterranean predecessors.
This sentence means that we are not sure whether these things are actually predecessors.
"¢ supposedly Mediterranean predecessors.
This sentence means that we are not sure whether these things are actually Mediterranean.
Similarly, In your sentence
A) recent extended sales slump - Here 'recent' modifies 'sales'.
B) recently extended sales slump - Here, 'recently' modifies 'extended'.
HTH