Yes, you can get it on every save file.
Here is an example.
Account 1's Primary Switch is the account you are downloading the DLC on.
Accounts 2-8 of the same Switch can all have the DLC as well, but they have to be connected to the internet to use it.
If Account 1 is on other Switch's, then you can redownload the DLC in the eShop for free, and you are treated the same as Accounts 2-8
To make a Switch a specific account's primary Switch, go to the eShop, click on your profile in the top right, scroll all the way down and you should see a button that either talks about registering or deregistering a Primary Switch.
I should note one thing.
- If two different accounts are using the DLC at the same time, then they will receive an error message that says something along the lines of "Two users are using the same downloaded content," or something like that. It sends you out of the game, but does not close it. If you are using Account 1's Primary Switch this message will not appear.
Source: Lots and lots of experience of having two Switch's used by two different people and trying to get my friend that uses an entirely different Switch some DLC so he doesn't have to pay for it.
Hope I could help and was not confusing.
It is not necroposting if the previous answer was wrong.