Early 1980s Sub - bi-directional bezel? Help!

[Antarctic Jamie]

A friend recently inherited this Sub from father-in-law who was known to have had it since the 1980s. There are some concerns he may have 'traded' it at some point and so I'm after some thoughts on whether it's genuine.

The first strange thing is that the bezel is bi-directional and has no ratchet or click, it just turns smoothly in both directions with a small resistance - have never heard of that on a Rolex. It also has quite a fine, almost sharp edge to the outside of the bezel ring.

It also has a really pronounced crystal that is several mm above the bezel.

Very grateful for any thoughts or input. I found one similar looking photo on the Internet but no real reference to a Sub with bi-directional bezel anywhere.

Many thanks. Photos attached.