For her to still be a Unicorn?  
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I have a SB that I met on WYP 7 years ago. She was and still is my 1st and best Unicorn. Filipina spinner, 5'1", 98 lbs., looks like high maintenance but isn't. Absolutely insatiable and willing to anything I want to do in bed. Loves to travel with me, asks for low sugar and even asks me to occasionally video her performing various acts on me for use on my "travel alone time".  
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The problem is her life and job make her only available 3 or 4 times a year for the last 3 years. It's maddening. I have many times cancelled standing SB sessions when she texts me that she in town and wants to meet. And I'll do it again willingly.  
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So, can I still call her a Unicorn?

...but recognize that you have a fortunate sex life 😋

The fact that she’s let it taper off over 7 years is great. It’s  also nice she’s kept her looks for that long.  

So far, my previous unicorns have always gotten jealous when I’m no longer banging the shit out of them at least once a week and they have started to ghost on me. I’d have to re open them with a high amount of money, probably,  to get their attentions back and it would never be like old times.  

My previous unicorns have also put on some weight. That might be because women change so much between 18-24, but none of them are still model material and I feel like I’ve been there and done that.

She sees me twice a week!!! In the Valley right?!?

But let me tap that when you can’t.  

treat every session as if it were the last, because you just never know.

 
I've have a few gals who were so fantastic in every way, that my biggest concern is that one day they won't be there - and sure enough, that's exactly what happened when one day you call their number and it's disconnected, or you never get a reply to their email, etc.

 
But then life can suddenly turn.  One day I was in the mood to clean out the old phone numbers on my cell phone, and came across a former unicorn who ghosted on me about two years earlier.  (Korean massage gal).   I decided, what the hell, let me just try the number one more time.   She picked up!   We were together in a few days time, and saw each other regularly for about another year and a half.   Then, the number went dead again.   That was about ten years ago.   I finally erased it just a few months ago.

 
But guess what?   Another unicorn contacted me about two months ago after several years of ghosting.   So far, it's been Platonic, except for some therapeutic massage.  (Her massages are a 10.), but I always loved just being with her as she is excellent company.   She has a clandestine boyfriend right now (married guy), so she is not interested in starting up that particular aspect of the relationship.   But I love to set up interesting situations, and I'm going to ride this one out and see where it goes.

 
Beats counting flowers on the wall....

Nice try, Tank.  :P

and has happened to me as well.  One of my favorites, ok maybe not exactly a Unicorn status SB, but still, she was a regular I dated all summer and truly enjoyed.  Then school started in September and she was too busy and stressed out to socialize.  After after 8 or 9 months I figured I'd never see her again.  But May rolled around and she called and said she'd gotten her life back on a better footing and would love to see me again.  That was nearly a year ago and we're still dating.  So don't ever erase those old phone numbers or email addresses.  You never know!

Its a good idea never to delete contact info, unless she did something so awful, you really don't want to see her again.  
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Imagine a favorite SB from the past that you really miss banging. She gave the best BBJNQNSCIMWS you've ever had, she loved to your tongue so much she could cum repeatedly for hours and then bring one of her friends over to as a present to Daddy. She had the tightest body you've ever seen, touched and fondled and she was zero drama, and always on time and fresh... then she ghosted or faded away for a time.  
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You finally give up on her and delete the contact from your phone.
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Time passes and then you get a text at 6 pm: "Missed you so much, I want to see you tongiht and swallow everything you've been saving for me, Daddy!'  
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You reply with "Who dis?"  
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Her reply:  "now you'll never no. lose my number, jerk"  
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Fortunately, I'll still have her number on my phone. So when she texts me 10 minutes later, I'll close that deal in about a minute.  
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Life is good.