There are a couple weird edge cases:
• Subsidiaries exist, but not multi-currency
• No subsidiaries exist (implying not multi-currency)
When I ran into this last year, there was not an easy way to get the base currency used on the NetSuite account using suiteql. Read from the currency table were blocked unless the multi-currency feature was enabled. In the first case, the subsidiary had a currency field but it was just an integer and there was no way to JOIN against the currency table sadly