After the combination of the financial crisis and covid-19, the EU's output will be 20%, or €3trn, smaller than if it had kept up the growth it managed in 2000-07. 

请教各位老师：

1. 这句话的主干是什么呢？

2. 如何理解had kept up the growth 这个过去完成时的使用呢？这个过去完成时是表示“与过去事实相反的虚拟”还是单纯地表示“过去的过去”呢？

这是前后段的内容：

Its budget deficits for 2021 average perhaps half of what America is planning. 

After the combination of the financial crisis and covid-19, the EU's output will be 20%, or €3trn, smaller than if it had kept up the growth it managed in 2000-07. 

The EU has suspended its deficit-limiting fiscal rules. Thanks in part to the ECB's monetary activism, European governments have the fiscal space to do more. They should use it.

以下是我的一些粗浅思考和疑问：

1. 第一种主干情况，：the EU's output will be 20%, or €3trn, smaller than it managed in 2000-07. 这个主干分析符合曹老师关于比较连词than的分析，因为than其实相当于output，并且做了manage的宾语。

但是，这一种主干分析有缺点，就是它导致对had kept up growth的理解有些棘手。如果than 后面的比较分句是it managed in 2000-2007，说明这个managed 就是现实发生的。那么if条件句是什么作用呢？就不需要假设了，无论这个if从句是虚拟语气还是普通的过去完成时。

2. 第二种主干情况：the EU's output will be 20%, or €3trn, smaller than if it had kept the growth。

这里把“ it managed in 2000-07”当做定语从句修饰growth。

但这种分析也有缺点。首先，than后面直接加if条件句是否符合比较从句的规则呢；另一个就是，如果是这样的话，为什么用had kept这个对过去的虚拟而不直接用对现在或者对将来的虚拟呢？

新的思考：

支持第二种主干分析：

尝试还原句子如下：

The EU's output will be 20% smaller than (the EU's output would have been) if it had kept up the growth it managed in 2000-1007.

或者

The EU's output will be 20% smaller than (the EU's output would be) if it had kept up the growth it managed in 2000-1007.

问题依然是：为什么要用had kept 呢？感觉还是用kept 或者would keep更符合语境？