Let's consider a pair of currencies, e.g. EUR -> USD. Are there one or several interbank currency exchange rates?
I see that both Revolut and OFX claim to use the interbank currency exchange rate, but when I look at their exchange rate, they differ slightly (e.g., currently, 1 EUR = 1.0935 USD on Revolut vs. 1 EUR = 1.0949 USD on OFX). I don't know whether this is due to quote lag or different interbank currency exchange rates.
There's no reason to think there's a central universal authority managing exchange rates between all the banks in the world. While some conspiracy theorists claim there's such an authority, I've seen no evidence of its existence. As your own empirical evidence suggests, there's more than one "interbank exchange rate", and my logic would suggest that there could be as many such rates as there are pairs of banks in the world trading in the currency.
The reason "interbank rate" is used for reference is because of large volume of trading between banks, compared to retail traders. As such, interbank rates are less susceptible to manipulation or influence.
