Users expected to "ignore" irrelevant parts of a form?

I have a web form that is split into several pages, it is an adaptation from a hard copy paper form, and the requirements are that the data captured should be the same.

For my webform I have asked for the users' salutation/first name/surname, I must also capture if they have a previous name.

The next page asks for their address, and also a previous address.

One thought that has been put forward is that most users won't have a previous name, so this field is largely redundant and therefore wouldn't need to be shown by default.

However, in my mind, if you are asking the user to action something "if" they have a previous name, then you are increasing the cognitive load when it would actually just be easier to ignore the part of the form that isn't relevant?

I will try and show you what I mean...

Or, perhaps it would be better to do some user testing to find out? Would a simple user test be the best way to find out what works best?