The short answer
Omega never released a watch called the "Seamaster 300 70th Anniversary." Two different names got mashed together in search listings. The Seamaster family began in 1948, so the 70th year was 2018, and Omega marked it with the Seamaster 1948 Limited Editions, two 38mm steel watches inspired by the original dress-sport Seamasters. The "Seamaster 300" name belongs to a separate branch: the 1957 dive watch, reference CK2913. Its own anniversary moments came in 2017 (60 years) and 2023, when Omega put a Summer Blue dial on a 41mm Seamaster 300 for the line's 75th birthday.
So when a listing claims to be a 70th anniversary Seamaster 300, one of three things is happening. Someone is describing the 1948 Limited Editions with the wrong name, someone is describing the 2023 Summer Blue with the wrong year, or someone is selling a counterfeit and borrowing anniversary language because it sounds collectible.
What the 2018 anniversary pieces actually were
I look at the 1948 Limited Editions as the real answer to this search. They are small, restrained, and nothing like a modern dive watch.
- 38mm stainless steel case, polished flanks with brushed surfaces
- Two variants: small seconds on calibre 8804, central seconds on calibre 8805
- Both movements are Master Chronometer certified by METAS, with a 55-hour power reserve
- Limited to 1,948 pieces per variant, which matches the birth year of the line
- Vintage-style dial with applied logo and leaf-shaped hands
- Anniversary engraving on the caseback
The limited number is the part that matters most here. Fewer than two thousand of each exist, each with box, papers, and a numbered certificate.
The 2023 Seamaster 300 Summer Blue
If the watch you have in mind has a blue gradient dial and a dive bezel, you are thinking of the 75th anniversary Seamaster 300 from 2023. It is 41mm, stainless steel, Master Chronometer certified, and not a limited edition. Omega built it as a regular production model. That distinction changes everything about availability and price.
Why a counterfeit of a limited edition is a bad bet
Counterfeit watches are illegal to sell and to import in the United States. They infringe Omega's trademarks, and customs will seize them. That is the legal side. The practical side is worse.
- A numbered limited edition has a matching certificate, and counterfeiters rarely get the number, the font, and the paperwork aligned
- Master Chronometer watches ship with a METAS certification card tied to the movement. That card is not reproducible with any accuracy
- Caseback engraving on the 1948 pieces is fine and shallow. Copies look stamped and heavy
- No counterfeit comes with a warranty, and no watchmaker will service it with genuine parts
- Water resistance claims on copies are marketing, not engineering. I would not swim in one
Resale is the quiet killer. A genuine 1948 Limited Edition holds value because the run was capped. A copy of it is worth nothing the day it arrives, and it will not fool anyone who has handled the real thing.
Better ways to get the look
If what you want is the vintage Seamaster feel, the honest routes are a current 41mm Seamaster 300, a pre-owned Seamaster 1948 from a dealer with papers, or a heritage-style diver from another brand. Buy the real thing used and you get the dial, the movement, the service network, and something you can actually pass on.