So it seems there are 28 bountiful delves per week across whole account that can give Brann XP.
You can check like that:
/run print(C_CurrencyInfo.GetCurrencyInfo(3142).maxQuantity-C_CurrencyInfo.GetCurrencyInfo(3142).quantity.." Bountiful Delves with Brann XP remaining.")
So it seems there are 28 bountiful delves per week across whole account that can give Brann XP.
You can check like that:
/run print(C_CurrencyInfo.GetCurrencyInfo(3142).maxQuantity-C_CurrencyInfo.GetCurrencyInfo(3142).quantity.." Bountiful Delves with Brann XP remaining.")