Why does MasterCook 2020 say it doesn't recognize some ingredients?
Open one of your recipes in MasterCook to the recipe edit screen. If you see a red circle next to an ingredient row, that means you linked that ingredient to one in MasterCook 15. See the screenshot example below.
MasterCook 2020 is not able to alter your recipes. We don't have access to your recipes. So, just as you linked an ingredient to an item in the MasterCook 15 ingredient database, you will have to unlink it so that version 2020 can use its own ingredient data instead.
Right click on a red circle and select Reset Ingredient Nutrition so version 2020 can use its own.
Below is a link to another article that you may find helpful.
What ingredients are included in MasterCook 2020? See this article.