Dear Gaveshika… if those people that you have come across are the type that tells any Tom, Dick or Harry that they meet that they are Sotapanna and Sakadaagaami, then you have nothing to fear. Only to such a person who has similar characteristics (gathi) as him/her, would a Sotapanna reveal that he/she is one such. By that what I mean is that, if an ordinary run-of-the-mill person asks you whether you a Sotapanna, you will evade that question, as this knowledge is something that you keep very close to your heart. So no fear, you have not committed an Aarya Upavaada.
But in case you had (even inadvertently) done a Aarya Upavaada to someone who walks this Noble Path that day, you could think about that person and ask for forgiveness. This is a very effective way to calm the mind and reduce tensions. If done sincerely, you should be able to see the effects in real life. You may notice that the tensions with that person is automatically reduced.
A person who treads this Path in all sincerity knows at every stage where s/he is at. One realizes that one is a Sotapanna, but it happens with time. When one observes oneself, it becomes clear to oneself that one has removed the characteristics (gathi) that prevents one from becoming such, and that you have attained that precious thing/stage sought by a Bhauddhaya (or a practicing Buddhist). Also, when you observe such characteristics (gathi) in a another (be it a much sought-after monk) you begin to question as to how that person could even be a Sotapanna. But you guard yourself and do not entertain such thoughts, as only a Buddha can say for sure whether a given person other than you, has attained magga phala or not. In this Path you will ONLY concern about yourself and NOT any other.
At this stage you do not need any guidance from another. You have seen the way to Nibbana (or a glimpse of Nibbana). You know what’s to be done, and silently you go about it, and your neighbours and others that you come across in your daily life will never know that you are one such (a Sotapanna). Once that knowledge that you have arrived at this stage of Sotapanna sinks in, your attitude, behavior, and outlook on life has changed forever.
Observing another person’s characteristics (gathi), you then get a feeling that there is a greater likelihood that the other person is at the Sotapanna stage or higher. ONLY with such a person would you share this kind of knowledge.