Please use the Question Tags to state the name and full version number of the Story Format you are using, as answers can vary based on this information. I will assume that you are using Harlowe v2.1.0
Each story project you create is assigned a unique identifier (known as a IFID), this identifier is embedded within each Harlowe 2.x based story HTML file you create, and it is used by the (save-game:) macro when it persists a copy of the game's current History in the web-browser's Local Storage area.
This is why the (load-game:) macro won't load the saves created in a different story, and why multiple story HTML files can use the same Slot Name when saving.
Making achievements in Harlowe
Global Stats - How do you create global stats that are shared between games?
There are a number of ways you can get around this limitation, two of them being:
The following example shows how to do the second method with the Global Stats related solution.
(set: _totalKills to GlobalStats.totalKills)
DEBUG: totalKills: _totalKills