Is it required to use the old URL in ID path? I thought that was just used for personal identification and you can fill in whatever you want?
Id path is just a unique identifier for the url rewrites. It has no actual logic in the redirect itself.
It is useful so you can mark certain rewrites for later use in the code.
For example, the urls generated for product pages have the id path
This way you can identify the product url rewrite via code.
It is also useful if you add your own module that writes entries to the
url_rewrite table. You can later retrieve them via code.
But an url rewrite will work even if the id path does not mean anything.
The only constraint is that it has to be unique per store view.
ID in Magento are used to refer the content, by the system. They have to be unique for that specific group. For example attribute ID, block Id etc. For Magento URL rewrite, you have to provide the Unique ID.
In the ID Path field, enter the unique identifier of the original URL. To redirect any page in your store, enter the relative path to the page. For example: brand/search/result/brandname