Third-cut folders have the idea of plenty of room for filing but try this.
Use fifth-cut and number them (starting at 1 or another number of your choosing). Number files in readiness, so you don't need to keep getting out your labeller. That said, numbers are quite distinct so hand-written wouldn't be difficult.
In a spreadsheet, have a column for the number, then another for the filename. Here you can write AS MUCH as you like, not just what will fit on the tab. Also, you can add a third column of keywords.
Sort by the second column and print it as an index. This serves to find a file without needing to access the computer.
This means, if you're unsure where to file something, it doesn't really matter. Choose where it's going and then add a keyword. For instance, if you have a car accident, does it go in the car, legal, medical or insurance file? Decide which makes most sense to you (ie which occurs first) and add the keyword accident. Alternatively, start a temporary file.
When files are emptied, the physical files stay where they are. When you re-sort the spreadsheet, the row is blank and so sorted as the first blank row under the existing files. Next time you need a new file, use the first empty one (looking at spreadsheet to see which is emptied).
There's no issue with where to put numbers and tabs are ALWAYS in sequence. It also means if co-workers don't work like you, they can add their own keywords.
I recently started working in a foreign office and adapted this system to have TWO filenames: one in each language.