"I've had a wonderful healing through prayer, but I can't write up a testimony because three members of The Mother Church didn't witness it—right?"
Don't jump to conclusions!
It is important that testifiers provide verification from three people who have firsthand experience confirming a healing. So, whenever possible, do provide their verifications for our records.
But when witnesses are not available we accept letters from Mother Church members in good standing who can vouch for a testifier's integrity and dedication to Christian Science.
The bottom line: you're always welcome to submit your testimony for publication.