Three a year is outdated.
In the past, docs used to do a series of 3 esi's in sequence. Patients were limited to 3-4 "series of 3" per year. This is different from your question, which is how many injections should be part of one procedure. I typically do one or two injections at each sitting, which covers the targeted area. In the past 10 years, I have 3 in one sitting twice. 5 is excessive.