Having done some further research here are a couple of things I have turned up which may help to validate authenticity of 93150 clasps. All of the images below are replicas found on Google Images and replica forums.
1. The 'better' replicas tend to be based on the later clasp design with lines on the fliplock:
2. They also tend to have more holes than the genuine ones (gen have 8). Genuine clasp also has a gap between the two 'sets' of 4 holes. You can see in above image more holes and no gap.
3. Some of the replicas have a more pronounced shaping for the thumbnail under the fliplock - this is never found on genuine clasps:
4. Some genuine clasps have a square depression past the last hole on the side at the opposite end to the fliplock (you can see this on my clasp in my original post) but this is never found of the replicas.
5. The 'better' replicas have a cut out on the inside side of the fliplock to avoid fouling on the rivets (circled below). The genuine fliplock is angled to avoid fouling on (smaller/neater) rivets and does not have the cut out.
6. Although placement of text to the right of the Rolex logo on the inside of the clasp is inconsistent on genuine clasps it is never right justified as can be seen in the image above.
These are just observations recorded here in case they're useful to anyone with the same question in future - please do feel free to correct me if any of them are incorrect and equally to add any others you may know of.
Thanks!