Sovereigns from 1917 and the surrounding WWI-era years are notable for being struck at Commonwealth branch mints — Sydney (S), Perth (P), and Bombay (I) — in addition to London, each carrying its own mintmark. This gives the year a genuinely different collecting dimension than most other dates: a "complete 1917 Sovereign set" can mean one coin per mint, not just one coin for the year.
Check for a mintmark on the reverse, below the shield, before buying a 1917 Sovereign — a coin with no mintmark is a London strike, while S, P, or I marks a branch-mint coin with potentially different scarcity and pricing.
Log the year, your cost basis, and photos — and see it valued at today's spot price alongside the rest of your collection.
Start tracking freeThey indicate the branch mint that struck the coin — Sydney (S), Perth (P), and Bombay (I) — as opposed to a plain coin with no mintmark, which was struck in London.
Scarcity varies by specific mint and mintage that year — it's not a blanket rule that all branch-mint coins are rarer, so check specific figures for the mint you're interested in rather than assuming.