Make the edge cases visible.
Leading zeroes, long numbers, Unicode, spaces, dates and formula-like text.
A small test. A clearer picture.
Imports can succeed while quietly changing your data. Send known controls through your workflow, then check what comes back.
Your control check
A passing result covers these control samples only. It cannot guarantee the integrity of an entire dataset. Possible causes are tentative.
Leading zeroes, long numbers, Unicode, spaces, dates and formula-like text.
Import and export the controls in an isolated area of your application.
No trimming, normalization or numeric guessing. Just what changed.