most places where you make an appointment now confirm by SMS and frequently ask you to reply yes or no to the appointment.
and I’ve noticed for places like dentist and similar that for whatever reason, the confirmation comes from a different number if not each time, then every two or three times.
of course I phone rather confirm via SMS if it’s a new number but the number and message is always legitimate.
Now, I don’t know why they use different numbers, but they do. And I don’t think scammers are going to keep using the same or same suite of numbers for precisely the reason that they’ll get blocked. So as I said, you get a rotation from scammers to legitimate numbers.
Now whatever you do obviously suits you, but I would say there’s a small chance that you would not receive an SMS that’s important because it’s a previous scam number and you’ve blocked it. YMMV.
in a related vein, I’m currently getting an avalanche of silly spam and phishing. Emails to my BigPond accounts. Ones where they vary the number of repeated letters and underscoring to get past any filter you might have set. As I’m getting out of BigPond emails as soon as I can make sure everyone is transitioned to my new one, I simply delete the Spam rather than trying to reset a filter for them.