Some servers operate on a "Seasonal" model. They wipe progress every 6-12 months. This is great for PvP balance but awful for collectors. Read the server's FAQ carefully. If they say "Season 4," expect your Baron rank to vanish next year.
Ironically, many private server owners are worse than the official publishers. Look for servers where the donation shop sells only cosmetics or convenience (storage slots). If a server sells "Enhancement Boosters +7" for $50, That server will shut down in 3 months after bleeding the whales dry. granado espada private servers