Short answer

Omega did not make a watch called the Seamaster 300 70th Anniversary. The Seamaster line began in 1948, so the 70th year was 2018. Omega marked it with the Seamaster 1948 Limited Edition, a 38 mm steel watch sold in two versions of 1,948 pieces each. The Seamaster 300 line began in 1957. Its nearest anniversary release is the Seamaster 300 60th Anniversary Limited Edition from 2017, limited to 3,557 pieces. Listings for a "70th Anniversary Seamaster 300" often mix the two releases, or put a 2018 label on a standard Seamaster 300 copy.

The anniversary models Omega sold

2018 Seamaster 1948 Limited Edition

  • Case: 38 mm, stainless steel
  • Production: 1,948 pieces per version (small seconds, central seconds)
  • Movement: Omega Co-Axial Master Chronometer, METAS certified
  • Dial: domed, with period hands and a 1940s case profile

Omega lists both versions on its own product pages. Read reference numbers and calibre numbers there, not from a reseller listing.

2017 Seamaster 300 60th Anniversary Limited Edition

  • Case: 39 mm, stainless steel
  • Production: 3,557 pieces
  • Dial: brown "tropical" finish with beige lume
  • Reference: 234.10.39.20.01.001

What a replica of these models is

A replica is an unlicensed copy. A factory that holds no Omega contract makes the case, dial, and bracelet. Movements come from third-party suppliers, in most cases Chinese automatic or quartz calibres. Case size can sit 0.5 mm to 1 mm from the genuine figure. Water resistance is a seller claim, not a test result. No replica carries a METAS Master Chronometer certificate, because METAS tests the finished watch and only Omega submits them. Caseback text is stamped or laser-etched. Limited edition numbers on a replica match no Omega record.

Points that show up in side-by-side photos

  • Case diameter and lug width
  • Dial text font and spacing, including the word "Seamaster"
  • Bezel insert printing and lume pip shape
  • Hand finish, at the edges of the syringe hands
  • Movement beat rate. Current Omega Co-Axial calibres run at 25,200 vph (3.5 Hz)
  • Caseback engraving depth and the limited edition number

Legal status in the US

Counterfeit watches are illegal to sell or import into the United States. Trafficking in counterfeit goods falls under 18 U.S.C. § 2320. US Customs and Border Protection can seize shipments and does so. A replica has no manufacturer warranty, no parts channel, and no dealer resale value. Service centers will not work on one. Any repair cost falls to the owner.

How to check a genuine anniversary piece

  • Caseback shows "Limited Edition" plus a number, such as 0112/1948 or 0913/3557
  • METAS certification card ships with Master Chronometer models built from 2015 onward
  • Reference number matches a page on Omega's own site
  • Box, card, and hang tag numbers agree with each other

What is not known

Sale prices for the 2017 and 2018 anniversary models move with condition and paperwork. Auction results are the public record with dates attached. Sellers of replicas seldom name the factory, the movement maker, or the case supplier. Those details cannot be confirmed from a product page.