If a recipe calls for 3 pounds of tomatoes, cored, should you start with three pounds of tomatoes and core them, or should you have 3 pounds after coring? I would have thought that you start with 3 pounds of tomatoes, but the gazpacho recipe I made tonight seemed light on tomatoes when I followed that logic.
Generally, assuming a recipe in English, if you see the word order "3 pounds of tomatoes, cored" you should assume that you start with three pounds, and then core them. If you see "3 pounds of cored tomatoes", it suggests you should weigh them after coring.
However, the first is still rather imprecise, as the amount of impact from coring could depend on the size and variety of tomatoes, and how severely you cut. The second instruction would be slightly less imprecise, though variables like the amount of skin on each tomato will depend on their size. So, if I were writing a recipe, I'm not sure I would choose the first wording unless I also specified a size grade of tomatoes.
If the recipe was carefully tested, it probably was carefully tested based on the ingredients available in the region the author was from at a specific point in time. I read about a historical recipe for that started with "3 ears of corn" or something along that line, and the cookbook author who rediscovered the recipe quickly realized that the size of 1980s ears of corn was much larger than 1800s-era ears of corn. So keep in mind that a recipe is going to leave a lot of knowledge unspoken and dependent on context that may not match yours. If you feel the recipe was light on tomatoes, use more next time. Eventually it will be your recipe, rather than the author's.