Is the 10th like the 11th?

R' Yochana and Reish Lakish have a machlokes in Nidda on daf 72b if the 10th day of the ziva cycle has the same halacha as the 9th day or as the 11th day. Reish Lakish maintains that the 10th day is like the 11th day. Rashi explains that the machlokes is about whether she requires shimur for that day.

The Aruch Laner asks why, according to R"L, didn't our Mishna (on 71b-72a) set up the machlokes as talking about the 10th instead of the 11th. He suggests maybe it's really a kula so it's koach d'hetera adif but he doesn't like that answer because it just as easily could have said that the machlokes is about the 10th and 11th. From the words of the Mishna, it definitely implies that the machlokes between Beis Hillel and Beis Shamai is specific to the 11th and not the 10th. According to Reish Lakish though the 10th has the same din as the 11th? The Aruch Laner doesn't answer the question.

I'm not sure if his premise is really correct. Maybe Reish Lakish doesn't mean to equate the 10th to the 11th completely with regard to all the gezeiros d'rabonon. He only means that m'doraysa she doesn't require a clean day if she sees on the 10th but that doesn't mean that the gezeiors d'rabonon are the same. Beis Shamai says in the Mishna that if the woman saw dam on the 11th day and then went to the mikva on the 12th during the day we are gozeir on the 12th because had the same thing happened during the 11 days it would have been tamei. However Beis Hillel says that we are not gozeir tuma in that case. The gemara explains that there is no need to be gozeir in that case because everyone knows that the 12th day is yemei nida so they won't confuse it. What happens if the reiya had been on the 10th day and not the 11th? I think that in that case Beis Hillel would be modeh with Beis Shamai that there is tuma d'rabanon. There the woman could get confused between the 11th and the previous days because she's not yet in yemei nida. Therefore, the Mishna could only discuss the 11th and not the 10th in the seifa so it did so in the reisha also. That would answer the Aruch Laner's question.