If you have written documentation (e.g., on a dealer work order) of a complaint within the warranty period that is addressed by the TSB, they'll usually cover it outside of warranty. For example, the if work order says "customer complains of whistling noise from sunroof - could not find anything abnormal", and there is later a TSB to fix something in the sunroof that makes a whistling noise, you should get coverage. Some of these things can be a judgment call.
My actual experience with this situation is with a 2000 MB ML320 that developed a very annoying problem of vapor locking and losing power when going over high/hot mountain passes. It was a very difficult to duplicate problem because of the specific circumstances, but when it bit, it bit hard and left me wheezing on the side of the road a few times. I complained several times and the numskull dealers replaced lots of stuff but for some reason refused to replace the fuel pump which seemed like the obvious problem. Well outside of warranty, I happened to see someone with the same problem on a forum like this and they mentioned a TSB (issued while my car was under warranty) described EXACTLY what my car was doing with the fix being a redesigned fuel pump and fuel filter. I marched into the dealer who proceeded to tell me that it would cost $2500 to get the TSB repair since I was out of warranty. I complained about how they totally missed the TSB when I was having the problem during the warranty period. They finally tried to weasel out of it by saying I was not maintaining the vehicle properly - I didn't have the fuel filter replaced at exactly the prescribed interval. I was going ballistic and finally got the fix covered if I was willing to cough up the regular charge for the fuel filter service (which was pretty expensive). It was a totally exasperating