 Solution

Not necessarily: structural sharing can make snapshots cheap, but the trait alone gives no storage guarantee. With a persistent data structure, unchanged portions of old and new sequences can be shared safely. Saving two root references costs $O(1)$ additional space per edit, and adjacent history entries commonly refer to the same intermediate version. With an appropriate balanced persistent tree, each positional edit may add only $O(\log n)$ new vertices, giving approximately $O(n+h\log n)$ storage for $h$ retained edits of comparable presentation size, plus references to slides.

There are important qualifications. A fully copied immutable array may allocate $\Theta (n)$ per edit and use $\Theta (hn)$ across its history. A persistent linked list shares suffixes but may copy a long prefix for a late positional edit. Moreover, snapshot history keeps old versions alive that an edit-specific inverse representation might otherwise release. Consequently a significant increase is possible with some implementations or workloads; it is not forced by saving Sequence references, and it cannot be ruled out from the interface alone.