Short answer: Excel and Google Sheets treat long ID numbers as math, not text. A registration number with a leading zero loses the zero. A 15-digit microchip number flips to scientific notation — and worse, the spreadsheet silently rounds the tail end to zeros, so the number is wrong, not just ugly. Format those columns as text before you export, and verify every chip and registration number survived.

What's actually happening

Two separate failures, same cause — the program assumes a long string of digits is a quantity:

  • Leading zeros vanish. A registration like 0045128 becomes 45128, because as a number the zero is meaningless. As an ID, it's a different dog.
  • Long chip numbers get rounded, not just reformatted. An ISO microchip number is 15 digits. Spreadsheets only hold about 15 significant digits of precision, so a number like 985112345678901 is displayed as something like 9.85112E+14 and the digits past the limit are replaced with zeros under the hood. Switching the cell back to "Number" format won't bring them back — the data's already gone.

That second one is the dangerous part. A reformatted number looks fixable. A rounded number is corrupted, and you won't notice until a chip lookup comes back empty.

How to prevent it

  1. Before you type, paste, or import chip and registration data, select those columns and set the cell format to Text.
  2. If you're importing a CSV, prefix the column or use the import dialog's "Text" column type so the program never tries to interpret the digits.
  3. In Google Sheets, set Format → Number → Plain text on the column first, then paste.

How to verify

Pick a handful of records and read the chip and registration numbers against your source — full length, leading zeros intact, no E+ anywhere. Do this on the way out of the old system and again after import. Two checks, both cheap, and they catch the one error that's nearly invisible once it's in.