When I first got my SM300 ....I took it to be a 1964 as I recall my Father got the watch roughly in that year. So 1964 it was, until I opened the back to read the serial # which according to the Omega serial # chart of 23 mil.....put the watch at the 1966 year. I have recently found some interesting information that seems to make some sense from another watch forum that may be of some interest to some other SM300 owners. Here is the following (quote) from that forum>>
(((((but to clarify the serial number, it appears from my experience that sm300's dont follow the same rules as most omegas in the same way that speedmasters dont.
I have owned 3 SM300's from 1964 and still own 2, a 165.014 and a 165.024 both stamped -64 after the reference.
All 3 of these have had 23 million serial numbers in them as has every -64 SM300 I've ever seen.
On that basis I would be confident in saying that yours is a 1964 model. A very nice family heirloom.))))) end quote. --------------Hope this may serve to clarify.......if indeed this information is accurate....cheers!

 

Thanks for that. So is yours stamped 64 after the ref? I wonder if the case stamp year number is always the correct indicator of the year (if it is the correct back of course)?

I have always assumed that the case back and the movement weren't necessarily from the same year cos the case may have been lying around a bit before the movement was put in.

 

My caseback is surely original....but is not stamped 64. Thanks for your reply...more on this watch>>
http://omegaforums.net/threads/seamaster-300-movement-from-60s.927/

 

Correct - the case back year only identifies the year the case was made, the serial of the movement is a very rough indicator of the year it was manufactured. +/- 2 years difference from the serial number charts is quite normal, although much more than that and you are probably looking at a replaced movement.
It is often seen from original guarantee/archive documents that a watch case stamped, say -64, would have been put together with the rest of the parts (Omega call it 'created') in 1965 or '66 and then not retailed until '67 or even later.

 

Been a while since I have been on forum, but work has had me globe trotting full time. I am hesitant to say I have also sold my Original Seamaster 300 as I am liquidating for an early retirement at 56 years of age, and in 41 days will be my last work period. Will be off diving the coral reefs of Asia, so see Yah's all on the flip side of life. Cheers