Credits are counted over rolling windows that heal continuously — the weekly figure is what you have used in the last 7 days, and the oldest of those searches drops out of the count exactly 7 days after you made it. There is no weekly or monthly billing date.
Read-only here. A key carries the same access this account has. If one is lost or you want it turned off, ask your operator — revoking takes effect on the next request. Only a key’s digest is stored, so a key itself cannot be shown again after it is issued.
Most recently searched first. This is your search history at artist level — one row per artist, however many times you have looked them up.