During my process (3+ years) whenever a doctor needed proof of RLE, the first thing s/he asked was, "Is Beth ____ ____ your legal name? When did you change it?" Some things require the use of one's legal name (contracts, accident reports, affirming surgeries, etc)
Nothing beats a court order showing gov't acknowledgement of your new identity...and really, nothing else is needed for RLE. Some fields (i.e., therapy) don't require legal proof, and can take your word.
Unless you're like me, trying to get a US passport and my birth cert last name doesn't match my previously used name, nor my new legal name...fortunately US State Dept said "if you can show you've used (previous last name, the one referenced on the court name change), we'll accept that." Turns out I'd kept all my expired drivers licenses for the past 20+ years, and that was sufficient (and a DD214 from 25 years ago).