The 42mm PO rep has been updated more recently than the 45mm PO replica. The 45mm has no s/n .. the 42mm adds a s/n but it is the same number for all watches.
Running serial numbers are a recent development, as FxrAndy says.
This is an World War 1 officer's Trench Watch .. it has a cover so that you don't smash the crystal mucking about in the trench, waiting for the signal to go over the top.
I have one here, but it's not a Rolex. Check eBay for "trench watch" to see hundreds of examples.
Here is the thread I made about it last week .....
The N-Factory submariner is a go-to piece for people who do not have a sack of cash to spend.
Available in A21j, Clone and genuine Swiss movements .. something for every pocketbook.
Please notice that this link contains normal Subs, LV Subs and Ceramic Subs.
http://www.timesshop...ce&orderway=asc
Every piece of leather is different, so your results can and probably will vary from mine, but you can see in this photo I took a moment ago, that the leather conditioning cream has taken the flat, uniform surface of the strap and added many areas of darker "freckles" .. and at least my Wife thinks it looks a lot less "plastic" in her words.