You should vote to close old questions which do not meet the current standards, for this as well as for other guidelines. Else, people only tend to get confused why their new question gets closed when they can point to an old, open question as an example.
As to whether a question meets the standards, this is a subjective decision. The Meta question you cite is still in force. So, for Culinary uses guidelines, only exceedingly rare ingredients, and typically-not-eaten ingredients are allowed. The kefir question falls under the first category, while questions about eating basil flowers fall into the second one.
Different people from different cultures have different knowledge of ingredients. So, it gets hard to judge which ingredient is rare and which one isn't. Somebody who grew up in Mexico might know dozens of recipes for nopales, while the average European is unlikely to even have heard the word. This is why it is extremely hard to judge what can fall under the first category. But if you search a large recipe site and get hundreds of hits for the ingredient, it is hurting the guideline.
If you are still not sure whether the ingredient falls under the guidelines or not, use your judgement. Don't forget that it is the community which shapes the rules, not the moderators; our main task is to combat inappropriate behavior by disruptive users and to provide support to users who have questions. On the larger sites of the network, most questions are closed by five community votes, not by a binding moderator vote - this is rare here on Cooking only because we don't yet have many users with voting privileges. But generally, if a question falls in a grey area respective a guideline, you shouldn't wait for more guidance from "above", but rather use your privilege as a community member to indicate your opinion, by casting a close vote for a question you feel is covered, or leaving a comment to a question which already has close votes but you feel should stay open. You are also encouraged to edit marginally good questions into better shape so they are a better fit.
For the three questions you linked in your question:
- The first one asks for the culinary uses of Chia seeds. The comments indicate that there are cuisines making extensive use of them (in this case vegetarian), so that it would be easy to find recipes and if left open, the question is likely to grow to an endless list of recipes, none better than the other.
- The second one is also about chia/flax seeds. It was edited to a wording which leads away from answers in the "list of recipes" format and to make it more general, asking about the important characteristics of the ingredient. The accepted answer is not a recipe. But if it starts gathering recipe-type answers, it will mean that the try to salvage it was not successful, and it should be closed.
- The third one is about kefir. A community member (who also happens to be a moderator) thinks that it is covered by the guideline, probably because kefir recipes are rare in his experience. If you think that kefir recipes are common, you are welcome to point this out and cast a close vote. The more convincing you are (e.g. by providing a large source of kefir recipes), the more likely it is that other users will agree with you and cast a close vote too. But if you agree that kefir recipes are rare, then it should probably stay open.
