Using of the indefinite article
There are two sentences with almost the same meaning:
"Steve and Brett both have a first class knowledge of the product..."
"...she is incredibly knowledgeable of her industry, with first class knowledge of her products..."
If the meanings of the sentences are not understandable enough, then I can place the hole ones. Just let me know, please.
Why the indefinite article was used with words "first class knowledge' on the first sentence and was not on the second one?
Is there some influence of the forms of the word "product" here? Why was the article used with an uncountable noun "knowledge"?