Q. I just learned that according to the Chazon Ish, as brought in Orchos Rabeinu, vol. 2, p. 94, one who said Today is the first day etc. is NOT yotzi sefiras haomer (he needs to say Today is one day, as opposed to first).
However, up until now I did not know this ruling of the Chazon Ish, whose rulings I am generally particular to follow, and have been counting “first,” “second,” and so on (as I count in English). May I continue counting in the future with a bracha, even though in the past I was (apparently) not yotzi?

A. Shulchan Aruch (O.H 489: 1) rules that on the first day of the sefira you count: Yom Echad – One Day (cardinal number) and not Yom Rishon – First Day (ordinal number). Divrei Shoul (Menochos 66) explains that since the Sadducees wrongly began counting the Sefirah on a Sunday which is referred to as Yom Rishon of the week, the term was changed by our sages to Yom Echad – Day One, which could apply to any day of the week.
If one counted Yom Rishon on the first day, Poskim rule that he complies after the fact. (Orchos Chaim 108 quoting Meorei Or and Divrei Hageonim 981, Nitei Gavriel, Pesach 3: 32: 1, Piskei Teshuvos 489 n. 21).
Both, Nitei Gavriel and Piskei Teshuvos also quote Orchos Rabbenu (2: 94). However, they understand that the reason the Chazon Ish said he did not comply bedieved, was because he didn’t have any intention to. The case was that one elder told his son after the shekia; tonight is the first night of sefira, and then the elder was in doubt if he could still count with a brocho that night. The Chazon Ish answered to his question; rishon is not echod, meaning that the words chosen, demonstrate that he did not have intention to count sefira at that time.
Horav Shlomo Miller’s Shlit”a opinion is similar, and you can continue counting with a brocho.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a