This is an exploded view of a Borg-Warner 3 speed, unfortunately without names for the parts:
http://www.amccf.com/tech/new/tranny_six_T-14.jpg
6.080-2 is the synchronizer sliding clutch and hub
6.090 is the blocking ring
6.144-2 is first speed gear
6.144-3 is reverse gear
The description I found for this transmission refers to 6.080-2 as a sliding clutch collar.
This
is a not particularly good image of an exploded view of another manual transmission, and illustrates the fact that in some cases the sliding clutch and hub, etc. is called a synchronizer.
Combine the two and you have the fact that the sliding clutch and hub assembly used on low / reverse (and in fact on any speed / gear) can in some cases be known as a “synchronizer”.
You appear to be hung up on the use of the word “synchronized”. I’m saying that the transmission uses synchronizers. That’s all I’m saying.