For the most part determining the appropriate balance sheet rate is fairly straight forward under ASC 830.
Data sources and timing of rate collection differ between companies but rarely are we challenged to review which rate we use, namely because it is unusual for two or more rates to be represented in the market place. A relatively new exception is the presence of CNY and CNH. US companies have generally identified the CNY rate to convert their Chinese assets and liabilities into USD.
Over the past few years China has eased its monetary policy and opened its currency markets by creating the CNH. The two rates demand an ASC830 decision, which Chinese currency rate, CNY or CNH is most appropriate for use in US GAAP financial statements. Bloomberg describes the CNY as a reference rate and not a rate at which a US company can exchange USD for Chinese currency. CNH on the other hand they define as a rate at which entities can exchange USD for Chinese currency albeit through Hong Kong. The two rates are rarely more than a few pips apart.