Tsinlien is Sea-Gull HK which was set up as a wholly owned but quite separate subsidiary in 2003 by Tianjin Sea-Gull.
My understanding (I could be wrong) is that Tsinlien S-G is intended *mostly* to be a seller of OEM branded watches, and was set up by Tianjin to fulfill that purpose, thereby leaving Tianjin the opportunity to produce entirely in-house pieces of higher quality directly under the Sea-Gull brand.
As I wrote in
this "The Watch Forum" (UK) post:
"the common version 1963 is a child of Tsinlien Sea-Gull of Hong Kong, not Tianjin Sea-Gull Watch Group.
Although the two companies have a close relationship, the common version 1963 was produced as an independent Tsinlien OEM product that kind of "took off" in the market in a few versions depending on order date, ordering company and so on. Don't get me wrong; there is no evidence that Tianjin Sea-Gull was in any way against the production, but it was just not a Tianjin product; it was a Hong Kong product."
WatchUnique has been a fairly long-term distributor of the legitimate Tsinlien product but there have been others.
For example, here are obvious 1963 variants sold by Colamer & Sons in Spain (some not available now, and others still are):
...and...
It's plain from many of the watches sold at
Colamer's website that they have a very close relationship with Tsinlien.
So, all of the legitimate (except legitimate D304 versions...I'll get to that) 1963 variants come from Tsinlien (not Tianjin) and are sold as whole watches by contract to various suppliers, some of whom market the watch as the 1963 Sea-Gull Air Force re-issue, and some who sell under their own brand (or sell both, like Colamer).
The seller named Thomas used to be an employee of Tsinlien). However, Tsinlien states that Thomas uses lesser quality parts for his pieces. The quality of the parts may or may not be second-rate, but it's probably worth noting that Tsinlien and Thomas are now competitors in the market. In any case, Thomas has enough connections to manufacturers (at least partly due to his past work with Sea-Gull HK) to produce generally well-regarded 1963 variants and other watches, like a few WUS CMW forum watches currently in -- or past -- production.
There is another 1963 variant: a commemorative and fully in-house beauty put out by Tianjin Sea-Gull at a higher cost (about $600), the D304, but it's sold out except for a few remaining in various seller's hands:

.
And so you can decide which version is the most accurate, here are the only photos of 1963s that I consider verified enough to be reliably called original PLA issued pieces:
...from Joel Chan's
Micmicmor site:
and from WUS moderator Gigfy:
Note the differences in hands, indices and crown in the originals, but it's known there were a few batches with differing cosmetics...