I am not sure if it matters, but I have removed several movies for various reasons. I don’t know if you can ever run out of index numbers, but there are lots of unused numbers now for the deleted movies.
I saw an online article saying they could be reindexed but it appears to be old option as I cannot see the functionality in my current app.
Don’t worry about the index number. You won’t run out, and if you don’t use them for anything there’s nothing the matter. It is a personal field and does nothing with the internal database or anything.
So: don’t worry about it.
This is how the index field works when all settings are default:
People use the Index numbers for stuff like putting stickers with a number on their DVDs (to easily locate them in their DVD room). Therefor, each Index number is only used Once.
When a number is deleted, the next added DVD will still increment on the last added DVD.
If you have #s 1,2,3,4,5,6,7,8,9,10
You delete #4
The next DVD you add will automatically be #11. #4 will not return.
If you manually change #11 to #4, the next DVD you add will be #12 - so you will be missing #11.
Re-indexing is something that the old Windows version can do, and our CLZ Movies Web version, but again, if you don’t use the index numbers for anything like the above, just ignore the number, nothing to worry about.
In fact you might like to just open the menu top left, go to Settings, then DISABLE “Show Index” - and then you never have to see it either 
I hope this information helps.