I was lucky enough that with T that it was by informed consent by I'm amusing that surgery always requires letter(s) (as that is what the WPATH standards of care say). But I can only really see a therapist qualified enough to give me a letter part of the year since I'm in college and I don't know if after a certain period of time of waiting that you would need a new letter.

Another question how can I be sure that my therapist can write me the letter?

Thanks.

One health system I know says the letter is good for 2 years.  Some hospitals and clinics have their own standards about who can write the letters, many require two for surgery but one for HRT.  Some may require a Phd level credential so it is best to check with the team you expect to utilize.

Good luck with the gatekeepers

I think it depends on who will be doing your surgery. All I needed was a letter from either my endocrinologist, or therapist stating that they were behind me on getting the surgery. In my case I had my endo do it. He did everything I needed for my surgery like my labs, my physical the only thing he couldn't do was a chest x-ray but he gave me a referral for that.

I never saw a therapist. I got a letter of recommendation for surgery from my same doctor who prescribed me T (through informed consent).

Not all surgeons will require a therapy letter.  The one I'm going to only requires one if you are not on hormones, otherwise they will take one from the hormone doctor. 

One place said the letter had to be within the last year. I forget which one though.

My understanding, for what it's worth, is that it's usual for the letter to be good for a year.