Two sites can report different supply figures for the same token, and the valuations built on them differ accordingly. The gap comes from decisions about which coins count as available.
Three different quantities are in circulation
Maximum supply is the ceiling written into the issuance rules, which some tokens have and others do not.
Total supply is how many exist right now, including coins held in locked contracts and treasuries but excluding any that have been provably destroyed.
Circulating supply attempts to count only those genuinely available to trade, which is the figure used in market capitalisation and the only one requiring judgement to produce.
Locked coins are the main deduction
Allocations to teams, early backers and ecosystem funds usually release gradually over years according to a vesting schedule.
Those coins exist and are visible on chain, but they cannot be sold until they unlock, so counting them as circulating overstates what the market must absorb.
Where vesting is enforced by a contract, the deduction is verifiable. Where it rests on a commitment by a company, the figure depends on that company's disclosure.
Judgement enters at the edges
Treasury holdings are contested. A foundation's reserve is not locked by code, yet treating it as freely circulating implies it might be sold at any moment.
Lost coins present a similar problem. They are unspendable in practice but indistinguishable on chain from ones simply held for a long time.
Providers apply their own policies to these cases, which is why supply figures diverge and why a change in methodology can move a token's ranking without anything happening on chain.
Unlock schedules matter more than the current figure
A token with a small circulating supply and a large locked allocation has a known stream of future supply arriving on dates set in advance.
Each release increases the amount that can be sold, and the effect on price depends on whether demand has grown to meet it.
Because the schedule is usually public, the arrival is not a surprise, but the size relative to daily traded volume is the number that determines whether the market can absorb it comfortably.
Fully diluted valuation answers a different question
Multiplying the current price by maximum supply produces a figure describing what the project would be worth if every coin existed today at that price.
It is useful for comparing projects with very different release schedules, since it removes the flattering effect of a small early float.
It is misleading if read as a valuation, because the coins are not there yet and the price used was set by trading in a much smaller pool of available supply.