@Aaron_Chaim, @DaasYochid,
I couldn’t find any mention of the Mahariv in the sources you gave, but the parenthesis next to the Rema (of haircutting Friday if Sunday is Lag) says the source is form the Maharil.
I think that if you hold “second half” of Sefira, you are not mourning for R’ Akiva’s Talmidim. You are mourning the slaughter of Ashkenaz in the Crusades.
R’ Moshe (??”? ?”? ??’ ??”?) says that according to all Shittos, the reason is for Talmidei Rabi Akiva, and that’s why there’s no problem of ?? ??????? when different people keep different days.