How do WhatsApp credits work?
A credit is not a message. It is used on the first successful send to a contact who did not start the conversation, and covers that contact on that number for 30 days. Writing to 3 contacts then sending each of them 2 follow-ups within 30 days therefore uses 3 credits, not 9.
A person who writes to you first, or verifiably shares their number, uses no credit. Importing a file does not either. Included credits renew each month and do not roll over; top-ups of 100 credits for €29 or 300 for €69 are shared across your numbers and valid for 24 months.
Having 200 credits does not guarantee 200 contacts in a month: the number's safeguards set the pace. They reduce risk but cannot guarantee that WhatsApp will never restrict a number.