Although Sea-Gull is now best known as a Tianjin Sea-Gull Watch Factory product, the earliest Hai Ou/海鸥/Sea-Gull branded watches were from at least two, if not more, of the Shanghai Watch connected factories, most notably 上海手表厂 (Shanghai [original/#1] Wristwatch Factory and 上海手表二厂 (Shanghai #2 Wristwatch Factory).
I've seen Hai Ou branded Shanghai built watches with SS1 movements (like mine, above), SM1A movements (usually seen in Diamond/Zuanshi brand watches), and with Tongji (Chinese unified/standard) movements.
The SS1 movement versions are the earliest.
These are not impossible to find, but they are much rarer than Tianjin's Sea-Gull watches.
Curator: Alberta Museum of Chinese Horology in Peace River; Member: China Horologe Association; Chief Expert: China Watch Overseas Working Committee (CWOWC); Sino-Canadian Horological Cultural Affairs...