My gut tells me they would be ignored, but to be honest, I have never taken that approach to importing price lists.

I have always exported the current items, updated the prices in Excel, then imported the list back in again.  That way I always have the proper file format.  Remember that prices can only have a maximum of 4 decimals, not 8 decimals displayed as four decimals in Excel.

To properly test your scenario, I would recommend doing the import on a copy of the company file first before you commit to the live file because then you can work out any problems before updating your live file.  Always have a current backup before you do any mass updates like an import.  They can go wrong very fast.

TimV said:

Do they just get skipped over or does the item get created and pricing added? 

In Sage 50 Canadian, the price list import tool cannot create inventory items.  It can just barely update selling prices if everything is perfect.

Bad data 'skipped over' is more like 'erroring out' and may eventually cause the process to run out of a system resource and crash, hang, or even start corrupting data.  I wouldn't rely on the item code matching process failing gracefully on say, 28,500 of 30,000 items - at best it will take a long time to run.

As Richard suggests, export the list first, you'll have something to check back on (or even to re-import the old prices with), and an excel report on which prices changed.  Better to use an Excel vLookup or similar function in Excel to match up the new prices to the item codes and build a price list in Excel, then export that sheet as a CSV, add the header and import.