Hmm. Well I don't know much, but I can share what I've experienced so far.
I use the pee pads and in theory it shouldn't help her (or me) to train her bladder to hold her pee longer, but I have noticed that as she grows older she does pee less amount of time. Nowadays in 24 hours (I change her pad once a day) she pees about 7-10 times a day. Before, the whole pad will be covered in these smalls spots of pee
Now we have several big spots. Also, I took her to the mountains 2 months ago and she held her pee with no problems for 4 hours in the car. During the night, after I fence her she will usually not pee until I wake up and put the fence away. And that ranges about 6-8 hours.
My other dog (well, my mom's dog before) Lulu was never really trained to pee outside the house but we do have a back terrace with easy cleaning, and she only goes there 2-4 times a day. I'm not really sure how to explain, but she was never really trained to "hold" it in but she just do. Lulu is 2 years old. Both sleep in the room with me
I guess what I'm trying to say is, with my dogs they seem to just do it naturally.