suggestion for help keeping track of foundables
currently, if you tap a foundable in your registry page, you will see (along with a brief description of that foundable’s relevance in canon) the date and general location of the FIRST time you received a fragment for that foundable.
i would suggest that the developers also add the date and general location of the most recent previous time, ie., the LAST time, you captured a fragment for that foundable. this will help you gauge exactly how rare (for you specifically) the spawn rate is for that foundable.
that information might be helpful to you in determining whether to use a certain potion, or not, in trying to capture a fragment in the next time you encounter it. for example, if i can see that it has been over 3-4 weeks since i last encountered the harp or the boggart cabinet, then i might just tell myself to spend the potion on it the next time i see it, even if ordinarily the threat (difficulty) level is not that big