Please explain tax-free childcare periods/limits

I opened the account on 25 July.

Deposited £2000, got HMRC Top Up £467.03 (why not £500?).

Now it says online (less than 3 months passed):

You can get a maximum government top-up of £467.03 for this entitlement period. You've £359.77 left for this period.

I don't understand, where is £359.77 coming from, is it still the first 3-month period or a new one has started ?

This all sounded so straightforward on paper - every 3 months, deposit £2000 - get £500 from HMRC. But in reality it is so confusing.

Thanks