Hi! I have migrated my collection data over from an app I had on a phone I no longer use. I'm very happy, but there's a feature that the old app had that I feel this collection management system could benefit from. On the old app, I could mark whether a game was owned (the default), in storage (so technically part of the collection but I know it won't be in my house if I am looking for it), sold or given away, or lost. I like that feature because I could include the DS games I lost at an airport (long story, left my whole DS case on a chair, ugh) in my collection, because I have owned them, but also have them not count towards my game totals. I also would not have to delete entries when I sell them; I could still have them listed for future reference without them counting towards the total.
Counting towards the total is the big part. Otherwise, you could just put that information in the Notes section (that is what I do for my games that are in storage). Maybe there could be a box you could tick to have it not count?