Typically inserts replace the note that has problems exactly where the problem note resides. To better understand this one should understand how exactly notes are produced and cut. When money is printed it is printed in a stack, where the notes with consecutive serials are found above or below the note, rather than next to the preceding or proceeding note on the same sheet.
When there is a problem with the printing of a sheet (and the problem is big enough to invalidate the entire sheet), the entire sheet is replaced where it was located in the stack. This is why normally you tend to find a (sheet) replacement note exactly where the next logical serial number note would have been, since once the problem sheet is replaced the entire stack is cut (straight down) to create bundles with consecutive serials.
On the other hand after all the notes in the stack are cut the bundles pass a secondary QC inspection, there will be times where production problems were not caught prior to cutting / sheet inspection. If such anomalies exist, and secondary QC notices it, then a single note replacement is used and inserted where the problem note existed.
Again the above is how printers typically dealt with problem notes in the past. There might be a small chance that they could change this (and place replacements elsewhere), but the likelihood of this is extremely small (but not impossible - aka it does happen that sometimes they are put at the end of the stack).
Also note that this printing/cutting method might be different as one printer likes to make non-consecutive (mixed) bundles.
