I have run into this problem with my own manga more often than I expected. I will be at a book fair, find a series I have already bought some volumes of, and suddenly realize I cannot remember how far I got. Do I already have volume 17? I feel like I bought 18 before. Or did I? And last time, was it volume 19 or 20? Remembering the title of a series is easy enough. Remembering the volume numbers of several series at the same time is a different story. It usually ends in one of two ways. I do not buy it because I am afraid I already have it. Or I buy it, get home, open the shelf and discover: I already own this volume.

The More Series You Collect, the Harder It Gets to Remember

With only one or two manga series, it is usually possible to remember where you left off and which volumes you own. But once you have dozens of series, the numbers start to add up. Some titles release new volumes months apart. Some you stop buying for a while and then start collecting again. At that point, memory becomes much less reliable. It gets even harder when the missing volume is not simply the latest one. Maybe you have volumes 1–12, you are missing 13, but you already own 14–16 because you found them second-hand or bought them out of order. Now remembering “I have up to volume 16” is not enough. And when you are at a busy book fair, surrounded by books and moving between different booths, you probably do not want to spend five minutes trying to picture the bookshelf at home.

The Easiest Solution Is to Stop Trying to Remember Everything

After this happened to me several times, I realized the real solution was not to get better at remembering. It was to have something I could check instead. For books, just having the title and volume number in a list is often enough. I can take out my phone and immediately see whether I already own that volume. A cover image makes it even easier. Some series have special editions, alternative covers, or later printings where the title alone may not tell the whole story. The list does not need to be a complicated database. If I can open it and answer one question— “Do I already have this?” —that is already useful.

This Problem Is Not Limited to Books

The same thing happens with many kinds of collectibles. Cards with multiple versions. Figures of the same character released in different editions. Toys that differ only by color or version. Games released for different regions. Or anything stored in boxes that we do not see every day. The larger a collection becomes, the less realistic it is to expect ourselves to remember every item from memory. Sometimes we do not buy duplicates because we collect too much. We buy duplicates because we can no longer see the whole picture of what we already own.

A List Becomes Most Useful at the Moment You Are About to Buy Something

For me, the real benefit is not just being able to sit at home and look through my collection. It is being able to check it while I am standing in front of something I am thinking about buying. If I can take out my phone, open my list, and immediately check whether that volume or item is already there, the decision becomes much easier. I no longer have to choose between: “I’ll buy it now and hope I don’t already have it.” and “Maybe I shouldn’t buy it in case it’s a duplicate.”

This Is Another Reason I Add My Collectibles to ROOMCOLLE

When I add an item to ROOMCOLLE, I do not see it as simply uploading a photo of something I own. It also becomes part of my own collection list. Which manga volumes I have, which figures I have already added, and which items I have already recorded are all things I can check again later instead of trying to keep everything in my head. The more consistently I add things, the more useful that list becomes as the collection grows. That does not mean I need to sit down and add everything in my home in one day. I can start with the things I am most likely to accidentally buy twice. For me, with books, that would probably mean series that are still ongoing and that I continue buying as new volumes come out. Then the next time I am standing at a book fair wondering, “Do I already have this volume?” I do not need to picture my bookshelf at home. I can just check.