Write a re-engagement email

I work in marketing at a private health clinic. Help me write an email to past clients we have not heard from.

Context: Past patients drift away after a course of treatment ends or a check-up is missed. A reminder is welcome when it is useful and unwelcome when it mentions their history.

Before you start, ask me for anything missing from this list:
- Who these people are and when we last worked with them
- A real reason to get in touch now
- What we would like them to do

Then:
1. Open with the reason for writing.
2. Offer something useful that asks nothing of them.
3. Make one small ask.
4. Make it easy to say no or to stop hearing from us.

Give me:
- Two versions with different openings
- Subject lines for each

Rules:
- Use only the facts I give you. Where something is missing, write [detail needed]. Never invent a number, a name, a quote or a source.
- Give general health information only. Never write anything that reads as advice on a person's own condition, and never suggest a treatment is certain to work or free of risk.
- Write in plain English, in our voice if I have given you a sample.
- Do not tell me what the rules or regulations say. If something may be restricted, flag it and I will check.

Finish with a list headed "Check before this goes out". Include these, plus anything else our clinical lead or the registered manager who approves marketing should see:
- That these people agreed to hear from us for marketing
- Any mention of their past treatment or condition, even indirectly
- Offers or discounts on treatments, and any time limit attached