Speaking about the euro area, it had a single monetary system for about six years. That is why time series study of macroeconomic data during this time period is not sufficient. It would also be very difficult to combine the post-ECB data with historical data. Firstly, many countries that have joined a single monetary policy do not have complete quarterly data on many significant macro series. For example most of the EU countries just dont have quarterly data for inventory investment and durable consumption. Looking from historical prospective, we can only analyze information from 1992 onwards. And such important issues as trade figures need to be analyzed through a longer period of time.
For example, quarterly data for inventory investment and durable consumption are simply not available for most countries. Furthermore, quarterly euro area trade figures net of trade flows within the euro area are only available from 1992 onwards. Thus, there are certain questions that cannot even be considered. That is why sometime sit might be better to analyze the member countries separately and only then make summaries and conclude information at the euro area level. Unfortunately this approach has also problems. First of all the data restrictions are considerable even at the country level. Second, we can not be quite sure how the member countries would react to common monetary measures because in the past there was no common monetary policy, so each country needs to adjust to new measures in its own way.
Overall, when analyzing euro areas data we have to be careful. There might not be needed information or it might be incorrect. Only specialists are able to conduct a good research and make some prediction based on them.