Been there, done that, got duplicates in the process.

Front pages being essentially variations on a theme, I usually lose track after volume 12 or 13. Ranma 1/2 was REALLY bad with some 40 volumes.

I did this with Chibi Vampire

Lost count of how many duplicates I ended up buying across the years...

Nowadays, I call my brother and ask him to check it up before buying, or vice-versa.