I may be able to shed some light on how Goodacre thinks Occam's razor ought to be used. He (and I) are heavily influenced by Michael Goulder, who used the term several times in his book Luke: A New Paradigm (1989). Goulder took the term paradigm from Thomas Kuhn, and he argues for a new paradigm (Luke's use of Mark and Matthew) to replace the old paradigm (Matthew and Luke independently used Mark and Q). In his first reference to Occam in the book, he wrote:
On the [old] paradigm we might have hoped that Q would preserve for us some authentic, individual tones of the Baptist; but the fact is, as I have illustrated, that the Baptist not only speaks with the same tones and phrases as Jesus, but with the same tones and phrases as the Matthaean Jesus. Some simple-hearted followers of Occam might be beguiled by this into reducing the number of hypotheses, since we now have too many. Since Q’s vocabulary and Matthew’s seem to be the same, and since sophisticated defenders of the paradigm will allow that Q is post 70, and so in the same decade as Matthew, and since Q also shares most of Matthew’s theology, it looks as if either Q or Matthew could go. Either Matthew wrote Q, or Q wrote Matthew. (pp. 14-15).
Goulder's point is that to be credible a hypothetical source has to be demonstrably different from an extant source, otherwise why hypothesize it in the first place? A hypothetical source can always offer at least as good an explanation as an extant source because we can always hypothesize it to have any characteristic the extant source has.
Frequently when i have argued that a certain characteristic of Luke's source is a characteristic of Matthew people who are not specialists in the synoptic problem (and some that are) ask: "How do you know it wasn't in Q?"
I don't. I can never know something was not present in a hypothetical source. My response, though, is usually to ask: so if Q looks like Matthew, how do you know the document you've been calling Q was not Matthew? Can you demonstrate that it was necessarily different from Matthew? If not, why insist that it's different from Matthew?
Best,
Ken