Since everyone who reads and writes any language on earth has "Hidden Memories":

It might be possible to store things in these "Hidden memories" for one purpose or another.

But, who would know what they were and what they mean?

Likely only those who put those memories in storage would likely know.

For example, this would have been one of the ways in order to create the 2nd timeline by storing enough information in people's minds to make this possible. You would want that information likely stored between 1900 and 2001 or possibly 1950 to 2001 in order to begin the 2nd timeline on 9-11-01 in order to prevent 5 billion people from dying like they did on the first timeline on 9-11-01. So, this would have been one of the useful ways to help create the 2nd timeline by storing enough information "out of sight" where it could be accessed in any way and at any time between maybe 1900 and 2001 on 9-11.

And since about 90% to 99% of humanity don't know or don't care that they have "Hidden Memories" they would be the perfect storage device. All one would have to do is to visit them in time when they were still alive and their brains still functional and working well.